In a large glass bowl, melt the butter in the microwave. Add the sugar, brown sugar, salt, extract(s), and eggs. Using a hand mixer, mix on high speed for 2 minutes. Add the baking powder, GF flour, and protein powder/extra GF flour and mix until fully combined. Scrape down the sides and bottom of the bowl with a spatula. Pour in the milk and mix until a smooth batter forms.