Preheat oven to 350 degrees f
Line baking sheet with parchment paper
Add chocolate chips and butter into a microwave-safe bowl—microwave in 2 30-second increments, stirring between each increment.
Stir chocolate chips and butter until the chocolate is completely melted in the butter. Add brown sugar, vanilla extract, and the egg and stir until smooth.
In a separate bowl, mix flour, cocoa powder, salt, and baking powder.
Add the dry ingredients to the wet ingredients mixture and form the cookie dough.
Form 3/4 inch cookie dough balls and arrange them on your cookie sheet.
Place one Reese's Piece into the center of each chocolate cookie.