PREHEAT oven to 350°F. Coarsely chop 8 oz. chocolate; set aside. Microwave remaining 8 oz. chocolate in large microwaveable bowl on HIGH 2 min., stirring after 1 min. Stir until chocolate is completely melted. Add sugar, peanut butter, butter, eggs, milk, and vanilla; stir with wooden spoon until well blended. Add flour and baking powder; mix well. Stir in chopped chocolate and peanut butter chips.
DROP rounded tablespoonfuls of dough onto baking sheets.
BAKE 12 to 14 minutes or until cookies are puffed and feel set to the touch. Cool on baking sheets 1 min. Remove to wire racks; cool completely.
TIP: TO freeze, wrap cooled cookies in plastic wrap; place in airtight container or freezer-weight resealable plastic bag. Freeze up to 1 month. Thaw cookies at room temperature before serving.