In a medium bowl, cream together peanut butter and butter.
Gradually blend in the sugars, eggs and vanilla; mix until fluffy.
Combine flour, baking powder, and salt; stir into the peanut butter mixture until well blended. Stir in chocolate chips, if desired.
Bake for 30-35 minutes in preheated oven, or until the top springs back when touched.
Cool, and cut into squares.