Rainbow cupcakes

Ingredients:

Cupcakes

• 1 and 3/4 tbsp. confectionery flour (a mixture of flour and starch)
• 1 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/2 tsp salt
• 2/3 cup whole milk, warmed to room temperature
• Finely grated zest of 1 lemon and juice of 1/2 lemon
• 1 tsp vanilla extract
• 170 g (12 tbsp) butter at room temperature
• 1 cup of sugar
• 3 large egg whites at room temperature
• Red, orange, yellow, green, blue and purple gel-based food coloring

Cream on egg whites

• 2/3 cup sugar
• 2 large egg whites at room temperature
• 1/4 cup cold water
• 1 teaspoon vanilla extract
• 1/2 teaspoon of tartaric acid salt (cream of tartar)
• A pinch of salt

Preparation:

1. Make the cupcakes: Preheat oven to 175°C. Line 12 muffin tins with parchment paper. In a small bowl, whisk together the flour, baking powder, baking soda, and salt; set aside. In a small bowl, whisk together the milk, lemon juice, and vanilla; set aside.
2. In a large bowl, beat the butter, 3/4 cup sugar, and the lemon zest with a mixer on medium-high speed until fluffy, about 5 minutes.
   
   Reduce the speed, divide the flour mixture into three portions, and the milk mixture into two portions, and fold them into the creamed butter, alternating them. Increase the mixer speed to high and beat thoroughly until smooth.
3. Beat the egg whites in a large bowl with a mixer on high speed. Gradually add 1/4 cup of sugar.
   
   Stir the resulting mixture into the prepared dough in two batches. Divide the dough into 6 equal portions; add 1-3 drops of food coloring to each portion and mix thoroughly.
4. Spread the purple batter into the bottom of the cupcake tins (about 1.5 teaspoons per tin), then the blue, green, yellow, orange, and red batter.
   
   Bake the cupcakes in the oven for about 20 minutes. Leave them in the turned-off oven for 5 minutes, then remove them and let them cool completely.
5. Meanwhile, prepare the cream: In a large metal bowl over a double boiler (do not let the bowl touch the surface of the water), combine the sugar, egg white, water, vanilla, cream of tartar, and salt.
   
   Without removing the bowl from the double boiler, beat the mixture with a mixer at medium speed for 5-7 minutes, until fluffy. Remove the bowl from the double boiler and let cool for 5 minutes. Fill a pastry bag fitted with a round tip with the frosting and frost the cupcakes.