Preheat oven to 350°. Spray or grease 12 muffin cups.
In a large microwave-safe bowl, combine sugar, butter, and water. Microwave on high for 1 minute or until butter is melted. Stir in 3/4 cup semi-sweet chocolate chips until melted. Stir in egg and vanilla extract. Add flour and baking soda, stirring until blended. Allow to cool to room temperature. Then, stir in 1/2 cup each peanut butter chips and semi-sweet chocolate chips. Spoon batter by heaping tablespoonfuls into muffin cups.
Bake for 13-15 minutes or until top is set and a toothpick inserted into the center comes out slightly wet. Place pan on wire rack. Centers of brownies will fall upon cooling. If not, tap centers with the back of a teaspoon to make a hole.
Place peanut butter in a small microwave-safe bowl. Microwave on high for 45 seconds, then stir. While brownies are still hot, spoon about a tablespoon of peanut butter into the center of each brownie. Top with semi-sweet chocolate chips and peanut butter chips. Cool completely in pan.