3 1/2cups/287g cake floursuch as Swan's down, do not substitute homemade cake flour
1Tbspplus 1 tsp baking powder
6large egg whitesroom temp
1 1/2cups/12.75 oz whole milkroom temp
1cup/113g unsalted buttersoftened
1 1/2cups/298g sugar
Pinkyellow and green food color
Buttercream and decors
1poundunsalted buttercubed, at room temperature
Seeds of 1 Tahitian vanilla bean
Blue food color
Confetti sprinkles for decorating
25Puffy Poles strawberry marshmallows
Preheat oven to 350 degrees. Grease two 6-inch pans and one 4-inch pan; line with parchment.
Sift together flour, baking powder, and salt; set aside. Whisk together egg whites and milk in a separate bowl; set aside.
Beat butter using the paddle attachment until soft and creamy. Add sugar gradually and beat until light and fluffy. Scrape down the bowl as needed. Beat in vanilla.
Add flour mixture alternately with the egg white/milk mixture. Begin and end with flour mixture and beat until smooth on medium-low speed after each addition.
Divide batter between three bowls evenly; color each bowl of batter with a food color. Divide batter between pans, pouring in different colors into each pan and swirling them gently with a knife or skewer. Bake 6-inch cakes at 350 for about 25-30 minutes. Bake 4-inch layer for 20-22 minutes. Let cool slightly in pan, then turn out and cool completely.
Buttercream and decors
Whisk together the egg whites, sugar, and salt in a large heatproof bowl. Set over the simmering water and whisk until the mixture is hot to the touch and the sugar has dissolved.
Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment.
Beat on low speed for 2 minutes. Increase to medium-high until stiff peaks are formed.
Continue beating at medium-high speed until the mixture is fluffy and has cooled (the mixing bowl should feel cool to the touch).
Turn the mixer off and switch from the whisk attachment to the paddle. Turn the mixer on medium-low and add the butter, a few cubes at a time, beating until well incorporated before the next addition. The egg whites will deflate and thin with the first few additions – don’t let this discourage you – keep going. It may also look curdled, but don’t fret. Beat on high speed when all the butter has been added. The mixture will thicken and become smooth after several minutes of beating. Beat in the vanilla bean seeds.
Transfer about 2/3 cup to a bowl and fold in one or two drops of blue food color. Transfer frosting to a piping bag fitted with a large closed star tip; set aside.
Fill and frost the cake layers with the remaining frosting. Stack the smaller tier, centered, on top of the larger tier. Place the marshmallows vertically around the entire bottom circumference of the large tier. Using the blue frosting in the piping bag, pipe decorative swirls along the tops of the marshmallows. Sprinkle the blue frosting with confetti sprinkles.
Snip the elastic on the candy necklaces and, while holding the two ends, drape it across the bottom of the smaller cake tier. Don't stretch the necklace! You want all of the beads to be perfectly lined up, and stretching will make them separate. Gently pat the necklaces into the frosting so they stick (I had to have a helper for this, it's not as easy as it sounds!). When all the beads are embedded into the frosting, gently pull the elastic string free and discard. If you need more beads to finish the line around the cake, snip another necklace and place the beads onto the cake with your fingers. Repeat the process with the remaining necklaces. You will have candies left over - but don't eat them! Safe them for the next step.
Pipe blue frosting stars around the top edge of the top cake tier. Place a candy bead on top of each piped star.