Preheat the oven to 350°F (175°C). Cut parchment paper for the bottom of two 9-inch cake pans and spray with gluten-free cooking spray.

In a large bowl, cream together the softened butter and granulated sugar with a mixer until fluffy.

Add vanilla extract, lemon extract, dried lemon peel, food coloring (optional), gluten-free flour, salt, and baking powder to the butter mixture and mix until combined.

Add the milk and mix until smooth.

Beat in the egg whites and mix on high for 2 minutes.

Pour half of the batter into the first 9-inch cake pan and the rest into the second 9-inch cake pan.

Bake on the middle rack for 25-30 minutes, until a toothpick inserted in the center comes out clean and the sides pull away from the pan.

Cool the cakes in the pans for about 10-15 minutes. Allow the cakes to completely cool before frosting.