HEAT oven to 350°F.
CHOP half the chocolate; set aside. Coarsely chop remaining chocolate; place in large microwaveable bowl. Microwave on MEDIUM 3 to 4 min. or until almost melted; stir until completely melted. Add butter; mix well. Add sugar, flour, baking powder and eggs; mix well. Stir in nuts and remaining chopped chocolate.
DROP 2 tablespoonfuls of dough, 2 inches apart, onto baking sheets sprayed with cooking spray.
BAKE 12 to 13 min. or until cookies are soft to the touch but tops are still slightly shiny. Cool on baking sheets 1 min.; remove to wire racks. Cool completely.
serving size = 1 cookie (33 g)