Combine peanut butter and butter in a large mixing bowl; beat well. Gradually add sugar, beating well. Add eggs, beating well. Stir in vanilla.
Combine flour, baking powder, and salt in a small mixing bowl; gradually add to peanut butter mixture, stirring well after each addition. Fold in chocolate morsels.
Spoon mixture into a wellgreased 9-inch square baking pan. Bake at 350° for 30 minutes. Cool completely in pan; cut into 1 1/2-inch squares.