Prepare Dough
Combine flour and baking powder.
Cream butter, brown sugar, and sugar.
Mix in peanut butter.
Mix in egg and vanilla extract.
Add flour mixture and beat until incorporated.
Bake Cookies
Preheat oven to 350F.
Roll dough into 1-inch balls.
Flatten balls with a fork in a criss-cross pattern.
Bake 10 minutes.
Cool completely on baking sheet.