Preheat oven to 350 degree F. In a medium saucepan combine sugar, butter, and cocoa powder. Cook and stir over medium heat until butter is melted. Remove from heat. Add eggs and vanilla; beat lightly with a wooden spoon just until combined. Add flour and baking powder. Beat until combined.
Spread batter in a greased 11x7x1-1/2-inch baking pan. Bake for 20 to 25 minutes or until a toothpick inserted near the center comes out clean.
Meanwhile, in a small, heavy saucepan heat caramels and milk over low heat just until melted, stirring constantly. Pour over warm brownies. Sprinkle with peanuts; press nuts lightly into caramel.
Sprinkle chocolate pieces over caramel; let stand until softened. Spread evenly. Cool on a wire rack. Chill. Cut into bars with a wet knife. Makes 24 brownies.