Heat oven to 350°F (if using dark or nonstick pan, heat oven to 325°F). Line 24 miniature muffin cups, 1 3/4x1 inch, with paper baking cups.
In large microwavable bowl, microwave butter, water and sugar uncovered on High about 1 minute or until butter is melted; stir until blended. Stir in chocolate chips until melted. Stir in vanilla and eggs until well mixed. Stir in flour and baking powder. Spoon 1 heaping tablespoon batter into each muffin cup.
Bake 17 to 25 minutes or until set (do not overbake).
Lightly press 1 candy bar on top of each brownie cup. Cool completely, about 30 minutes.