• Oven & Pans - Preheat the oven to 350°F /175°C/ Gas Mark 4 and prepare two 9-inch round cake pans, three 7-inch round cake pans, or four 6-inch round cake pans with parchment paper and nonstick spra
• Dry ingredients - Whisk together the flour, baking powder, baking soda, and salt in a separate bowl.
  2¾ cups All-purpose flour, 2 ½ tsp Baking powder, ½ tsp Baking soda, ¼ tsp Salt
• Wet ingredients - Cream the butter and sugar in a large bowl until light and fluffy. Beat in the egg yolks one at a time. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream and lemon juice. Mix in the lemon zest, yellow food color, and vanilla extract.
  1 cup Unsalted butter, 2 cup Granulated sugar, 4 large Eggs, 1¼ cup Sour cream, ½ cup Fresh lemon juice, 2 tbsp Lemon zest, 1 tsp Vanilla extract
• Whip whites - In another bowl, beat the egg whites until stiff peaks form. Gently fold the whipped egg whites into the cake batter until just combined.
• Bake - Divide the batter evenly between the prepared cake pans and smooth the tops. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
• Cool - Allow the cakes to cool in the pans for 10 minutes, then remove them from the pans and transfer to a wire rack to cool completely.

Assemble

• Lemon frosting - In a large bowl, beat the butter until creamy. Gradually add the powdered sugar, alternating with the lemon juice, until smooth and creamy. Add more lemon juice, yellow gel food color, or milk if needed for a spreadable consistency. Stir in the lemon zest.
  1 cup Unsalted butter, 4 cups Powdered sugar, 2 tbsp Fresh lemon juice, 1 tsp Lemon zest
• Stack - Once the cakes are completely cool, frost the top of one cake layer with a layer of frosting. Place the second cake layer on top and frost the top and sides of the cake with the remaining frosting.
• Piping - Place the remaining frosting in a piping bag with a rose petal tip. Pipe horizontal swirls on the sides and top of the cake.