1. Heat oven to 350°F. Line 18 muffin cups (2-1/2 inches in diameter) with paper or foil bake cups. Remove wrappers from chocolate pieces.
2. Place butter in large microwave-safe bowl. Microwave at HIGH (100%) 1 to 1-1/2 minutes or until melted. Stir in sugar and vanilla.
3. Add eggs, one at a time, beating well with spoon after each addition. Add cocoa; beat until well blended. Add flour, baking powder and salt; beat well.
4. Remove 1-1/4 cups batter; set aside. Divide remaining batter evenly into muffin cups. Place one chocolate in center of each cup. (Do not push into batter.) Place slightly rounded tablespoon reserved batter on top of each chocolate.
5. Bake 18 to 20 minutes or until surface is set. Cool completely in pan on wire rack. Garnish as desired. 18 brownie cups.
VANILLA CUPS: Use 1 cup packed light brown sugar and 1 cup granulated sugar in place of 2 cups granulated sugar; eliminate cocoa and increase flour to 2-1/2 cups. Follow above directions.