Preheat the oven to 350F/175C.

Grease two 9-inch cake pans or three 7-inch cake pans with vegetable shortening. Line the bottoms and sides of the pans with parchment paper. Set aside.

In a large bowl, cream together the butter, sugar and dry strawberry gelatin until light and fluffy. Beat in eggs one at a time, mixing well after each addition. Combine the flour, baking powder and salt; stir into the batter alternately with the milk. Blend in vanilla extract and strawberry puree. Add the food color, if using, and mix again until consistently pink. Fold the confetti sprinkles into the batter and immediately divide the batter between the prepared pans.

Bake for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cakes to cool in the pans for 10 minutes before turning them out to cool completely.

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 3/4 cup frosting to a piping bag fitted with a large open star tip. Fill and frost the cake layers. I used about 2/3 cup to fill each 7-inch cake layer, or use 1 1/3 cups to fill a 9-inch layer.

To decorate the bottom of the cake with confetti sprinkles, place the cake (on the cake stand/serving plate) inside a large baking pan. Toss a handful of sprinkles onto the cake allowing the excess to fall back into the baking pan. Repeat process around the entire lower circumference of the cake. Brush excess sprinkles off the bottom of the cake plate with a pastry brush. Pipe stars around the top edge of the cake with the reserved frosting in the piping bag. Pipe one large frosting swirl in the center of the cake and garnish with a white chocolate-covered strawberry half.

Store the cake in the refrigerator loosely covered in plastic wrap. Bring to room temperature before serving.