Melt butter in a large, microwave safe bowl in 15-second increments (stirring between) until butter is melted. Make sure butter is not too hot- my tip is stop microwaving when the butter is mostly melted, and stir until it is fully melted but not hot.

Stir in sugar.

Add eggs and vanilla extract. Stir well.

On top of the wet ingredients. Add flour, cornstarch, baking powder and soda, and salt. Whisk dry ingredients together and then stir to combine with wet ingredients.

Stir in sprinkles. Refrigerate the dough for at least 30 minutes.

Preheat oven to 350F and prepare cookie sheets with cooking spray or parchment paper.

Use a cookie scoop to form dough balls of about 2 tbsp. Press tops of balls into extra sprinkles if desired.

Place at least 2 inches apart on cookie sheet and bake on 350F for 12 minutes- don't over bake!

Allow cookies to cool for 5 minutes on cookie sheet before transferring to wire rack to cool completely.