Rainbow cake with cream

Ingredients:

Cakes

• Flour-based cooking spray to spray the pans
• 6 and 1/4 cups sifted premium flour
• 3 tbsp. baking powder
• 0.5 tsp fine sea salt
• 2 and 1/4 cups whole milk
• 2 tbsp vanilla extract
• 1 and 3/4 cups (380 g) unsalted butter, room temperature
• 2.5 cups granulated sugar
• Whites of 10 large eggs at room temperature
• Red, orange, yellow, green, blue and purple gel food coloring

Swiss Meringue Buttercream

• Whites of 12 large eggs
• 2.5 cups granulated sugar
• 1/4 teaspoon fine sea salt
• 1100 g unsalted butter, diced, at room temperature
• 1 tbsp vanilla extract
• 1.5 cups of multi-colored confectionery sprinkles
• 24 round chocolate candies in multi-colored glaze
• 1 tbsp. multi-colored nonpareils

Flags made of mastic

• 2 and 2/3 cups mini marshmallows
• 2 cups sifted powdered sugar + extra for working with the fondant
• 1 tbsp. of confectionery fat
• Red, orange, yellow, green, blue and purple gel food coloring
• Special equipment: six 2cm round cake pans; candy thermometer; piping bag fitted with a small star tip; spatula; scraper or icing spatula; rubber gloves; 4cm triangle cookie cutter.

Preparation:

1. Preheat oven to 350°F (175°C). Spray 6 8-inch round cake pans with cooking spray (or grease and flour the pans).
2. Sift the flour, baking powder, and salt into a large bowl. Combine the milk and vanilla in a large bowl fitted with a liquid spout. In the bowl of a stand mixer, beat the butter on medium speed until smooth. With the mixer running, gradually add the granulated sugar and beat until the mixture is light and fluffy, about 3 minutes. Reduce the mixer speed to low and add the flour mixture in 3 additions, alternating with the milk mixture. Begin and end with the flour mixture. The dough should be smooth.
3. Cakes:
   
   This protein cake requires a lot of egg whites, so stock up! In a perfectly clean bowl, beat the egg whites on high speed until stiff peaks form, about 5 minutes. Gently fold the egg whites into the batter in 3 batches.
4. Place 2 cups of batter into 6 separate bowls. Tint each portion one of the rainbow colors. Gently stir with a spatula to prevent the batter from collapsing and leaving white streaks.
5. Divide the batter among the prepared pans and bake until a toothpick inserted into the center comes out clean, about 20 minutes.
6. Place the cakes on a wire rack and let cool completely. Once cool, trim off any raised tops with a serrated knife.
7. Swiss Meringue Buttercream:
   Place a saucepan one-third full of water over medium-high heat and bring to a boil. In a large heatproof bowl, combine the egg whites, granulated sugar, and salt. Place the bowl over the simmering water and whisk until the mixture is hot to the touch and the sugar has dissolved (120-140°F on a candy thermometer). Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat on low speed for 2 minutes. Then beat on medium-high speed until stiff peaks form. Continue beating at medium-high speed until the mixture is fluffy and cooled (the bowl should feel cool to the touch).
8. Turn off the mixer and switch to the paddle attachment. Turn the mixer on medium-low speed and add the butter a few cubes at a time, beating until fully incorporated before adding the next one. Add the vanilla extract. Beat on high speed until the frosting is thick and completely smooth.
   
   
   When making the frosting, after adding a few pieces of butter to the whipped egg whites, the mixture will collapse. The mixture will resemble curdled milk, but don't let that discourage you. This is just one of the unpleasant stages the buttercream must go through before it turns into a beautiful, fluffy icing.
9. Assembly:
   
   Transfer 1 cup of frosting to a pastry bag fitted with a small star-shaped tip; set aside. Pipe a small amount of frosting onto each cake layer. Begin assembling the cake with the purple layer at the very bottom. Cover it with a thin layer of buttercream frosting, then add the blue layer. Continue alternating cake layers and frosting with the remaining green, yellow, orange, and red layers.
10. Place the layers on top of each other, checking that the cake is level on all sides and not tilted or wobbly. If it seems a little wobbly, try piercing it with a long plastic straw or wooden skewer to stabilize it. Insert it through the center of each layer of the cake. Simply trim the straw or skewer to the height of the cake.
11. Glaze:
    Cover the entire cake with icing and smooth it out.
12. Place the cake on a large platter and use your cupped hand to press down on the sprinkles, allowing any excess to fall onto the platter.
13. Repeat until the bottom two-thirds of the cake is tightly covered with sprinkles. Refrigerate the cake.
14. Mastic:
    
    In a large microwave-safe bowl, combine the marshmallows with 1.5 teaspoons of water. Microwave in 30-second intervals at 100% power, stirring occasionally, until melted and smooth, about 1 minute.
15. Add 1 cup of sifted powdered sugar to the melted marshmallows and stir until fully incorporated. The fondant will become quite thick and difficult to stir. At this point, put the spoon aside and get ready to use your hands.