PREHEAT oven to 350° F.
COMBINE flour, cocoa, baking powder and salt in small bowl. Melt 1 cup morsels in a small, heavy-duty saucepan over low heat; stir until smooth. Beat sugar, 1/3 cup peanut butter, butter and vanilla extract in large mixer bowl until creamy. Beat in melted chocolate. Add eggs, one at a time, beating well after each addition. Gradually beat in cocoa mixture. Stir in remaining morsels. Cover; refrigerate just until firm.
SHAPE dough into 1 1/2-inch balls; press thumb into tops to make about 1/2-inch-deep depressions. Place 2 inches apart on ungreased baking sheets. Fill each depression with about 1/2 teaspoon peanut butter.
BAKE for 10 to 15 minutes or until sides are set but centers are still slightly soft. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.