This cake holds a colorful surprise inside! Galaxy blue, green, and purple hues are swirled in tangy buttermilk cake batter. The cake is wrapped in a night sky of black fondant with zodiac constellations painted on using white food color.
The Autumnal Equinox is on the horizon and if you’re a fellow sky gazer, then you may have noticed signs of the season’s change. Here in my corner of the world (Northern Hemisphere), daytime brings a shade of brilliant blue that is only visible in fall. Indoors the shadows move across the windowsills differently. Crisp nights make it easy to examine a new (old) set of constellations that have moved across the sky and have different orientation.
The whole thing makes me wax philosophical. I suppose looking at the night sky will do that. It made me consider the zodiac, which I’ve never put much stock into, but have on occasion nodded my head when someone explains the behavior of a Scorpio or Cancer. Each sign supposedly describes characteristics of each and every human being on earth. I’ve decided it’s not such a stretch. My baker’s brain chalked it up to this: We’re all different slices from the same cake – why not? Sound overly poetic? Yet another side effect of star-gazing. As is this cake.
I’ll begin at the beginning, which is a cake batter I refer to as ‘Galaxy Swirl’. What does a galaxy taste like? It’s tangy. I used my favorite vanilla-white cake recipe (it tints well with food color) and added a big dose of buttermilk. It makes for a beautiful cake crumb that slices like a dream.
The exterior of this cake is made with a great product made by Wilton: Decorator Preferred Fondant. If you’re a fondant novice, then start with this stuff. Seriously. As long as humidity isn’t high, you can roll it out without dusting or greasing your work surface. If you’ve ever tried to tint white fondant black with food color, then you know what hassle it is (I only ever achieve dark gray). I recommend buying ready-made black fondant because it will make this project easier and much more enjoyable.
If you’re new to covering cakes with rolled fondant, you should certainly read this tutorial. My cake is a 7-inch round triple layer cake covered in vanilla buttercream and black fondant. This is our primed canvas, so to speak. It seems I’m always making a case for the 7-inch cake – yes, you’ll need these pans or at the very least, this 7-inch pastry ring to trim 9-inch cakes to size – but smaller cakes are much easier to cover with fondant than larger cakes. I recommend starting small, especially if you are a beginner.
Painting this cake was so much fun! You’ll need a small fine-tipped artists’ brush. My old art professor would say “use the brush for painting the reflection of light in a grasshopper’s eyeball”. That is to say, a size zero or one round-tipped brush. You’ll also need paint, and that comes in the form of bright white gel food color. I used a small plate turned upside-down to lightly score a circle into the top of the cake, and then a straight edge to make a line through the middle. The circle is the earth’s pattern around the sun and the line points to your choice of constellation or between two. I visited NASA’s website and Universe Today to get pictures of constellations and zodiac symbols. You can find the top cake illustration here and this illustration was helpful for painting constellations on the sides of cake. The symbols and lines I used aren’t too difficult to free-hand with a paint brush. For the constellations, I literally played connect the dots; drew ‘stars’ and connected them.
You’ll also need a large-ish stiff bristle brush. Any large hog bristle brush will work (and no, I don’t like the description hog bristle any more than you do). Dip the brush into the white food color, and then pull back the bristles with a finger and flick the paint onto the cake holding the brush about 4-inches from the cake’s surface, until the cake is speckled with white ‘stars’.
Cutting this cake is a real show-stopper! I love that each slice is unique, both inside and out. The brilliant swirly cake colors are attributed to a combination of Betty Crocker’s gel food colors in bold, neon and classic. You can find them at the links provided, but you’re likely to find them priced more affordably at your local grocery store.
The paper chalkboard picks are from Target, but I bought them so long ago I’m not sure they’re still available. You can find similar picks here and here. I used the white food color to paint the zodiac names, and then placed the picks on their corresponding symbol.
I think this cake would be great for any solstice party (outdoors under the stars, weather permitting) and for – what else? – birthdays!
Zodiac Constellation Cake
Galaxy swirl cake batter
- 3 1/2 cups cake flour
- 1 Tbsp. plus 1 tsp baking powder
- 1/2 tsp salt
- 6 large egg whites room temp
- 1 1/2 cups buttermilk room temp
- 1 cup vegetable oil
- 1 1/2 cups sugar
- 2 tsp vanilla extract
- Betty Crocker Bold: dark blue food color
- Betty Crocker Classic: blue and green food colors
- Betty Crocker Neon: neon purple food color
Frosting, fondant and décor supplies
- 1 recipe American buttercream link
- 24 ounces black ready-made fondant I recommend Decorator Preferred
- Fondant smoother such as Easy-Glide Smoother by Wilton
- Americolor Bright White gel food color
- Fine-tipped artists brush round size 0 or 1
- Large stiff bristle brush round size 4 or larger
- Black paper chalkboard picks if using
- Make the cakes: Preheat oven to 350 degrees. Grease three 7-inch cake pans (or two 9-inch cake pans) and line the bottoms with parchment circles. Sift together flour, baking powder, and salt; set aside. Whisk together egg whites, buttermilk, oil, sugar and vanilla in a separate bowl; set aside.
- Add dry ingredients to wet ingredients in three additions; beat until smooth on medium-low speed after each addition.
- Divide batter between three bowls. Tint one bowl with neon purple food color and mix until a vivid color is achieved. In a second bowl add equal additions of classic blue and green gel food color; mix until a vivid turquoise color is achieved. In a third bowl tint the batter with bold dark blue food color; mix until well combined. Place large spoonsful of each color batter in the pans, alternating them often so that the colors are well varied. Use a skewer to swirl and marble the batter. Bake the cakes 350 for 25 to 30 minutes, or until a toothpick tester inserted in the centers come out clean. Let cool slightly in pan, then turn out to cool completely. Level each cake with a serrated knife or cake leveler.
- Frost the cake: Fill two cake layers each with 1/2 cup frosting. Stack the cakes, ending with the plain layer on top. Frost the entire cake with a thin layer of frosting (crumb coat) and refrigerate until firm, about 30 minutes. Cover the cake with another thicker layer of frosting making it as even as possible (find my tips here in this video) and chill the cake again until the frosting is solid, about 30 minutes.
- Fondant work: Before rolling out fondant, knead it until it is a workable consistency. If fondant is sticky, knead in a little confectioners’ sugar. Roll the fondant out into a large circle with a large rolling pin to about 1/8-inch thickness (you can also roll to 1/4 inch, thicker fondant is less likely to tear, but will create rounded edges on your cake). To keep fondant from sticking, lift and move as you roll. Add more confectioners’ sugar if needed. Gently lift fondant over a rolling pin; position on cake. Shape fondant to sides of cake with Easy-Glide Smoother. I recommend using the Smoother because the pressure of your hands may leave impressions on the fondant. Beginning in the middle of the cake top, move the Smoother outward and down the sides to smooth and shape fondant to the cake and remove air bubbles. If an air bubble appears, insert a pin on an angle, release air and smooth the area again. Use the straight edge of the Smoother to mark fondant at the base of cake. Trim off excess fondant using a spatula or sharp knife. Your cake is now ready to decorate.
- Paint the cake: Use the zodiac symbols and constellations templates linked in the blog post as a guide for painting the cake. Score a circle on top of the cake with a fondant tool or the dull edge of a butter knife, so that it’s within 1 1/2 inches of the cake’s edge. Use a piece of paper with a straight edge to score a line through the center of the circle. Using the fine-tipped paint brush and undiluted bright white gel food color, paint a perforated line in the scored circle. Paint a perforated line on the straight edge line, and then paint an arrow at one end and two arrow marks anywhere inside the circle. At the other end of the straight edge line, paint a circle (earth). Paint zodiac symbols around the top edge of the cake, outside the perforated circle. Have a small cup of water and paper towels to clean your paint brush when needed. If you make a mistake, use a little of the water on a paper towel to ‘erase’ the white food color (I ended up removing an entire constellation on the side of the cake and re-painting it!). Paint constellations corresponding to the symbols on top of the cake on the sides of the cake. I painted dots for ‘stars’ and then connected them. Take your time and paint the connecting lines as thin as possible. They’ll look best this way. Now, the messy bit: Dip the hog-bristle brush into undiluted white gel food color and pull the bristles back with your fingers. Flick the paint onto the cake holding the brush about 4-inches from the cake’s surface, repeating the process until the cake is speckled all over with white ‘stars’.
- Allow the cake to air dry for 45 minutes before serving. If using the chalkboard picks, use white food color to paint zodiac names on them, and place the pics on top of the cake and on their corresponding symbols.
- Cover lightly in plastic wrap and store at room temperature for up to 3 days.