Preheat oven to 350 degrees F (175 degrees C) and line your baking pan with cupcake liners.
Beat butter and 1 cup of sugar with an electric mixer in a large bowl until light and fluffy (about 2 minutes).
In a separate mixing bowl, beat egg yolks (save egg whites) and combine with butter mixture.
Sift together flour and baking powder. Alternate adding the flour mixture with the milk to the butter mixture. Beat well and add vanilla extract.
Beat egg whites until stiff and stir together with 1 cup of sugar. Fold this into batter.
Fill each cupcake liner 2/3 full and bake until golden brown (about 24-28 minutes). Oven times can vary so check cupcakes often.
For the cookie dough:
Cream together butter and sugar. Add vanilla and salt.
Add flour and mix to combine.
Add milk and chocolate chips and stir until consistency is cookie dough-texture.
Roll into small balls. Fill into the center of each cupcake (use a small knife to cut out little holes – see photo).