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Preheat oven to 350°. Spray or grease 12 muffin cups. *(or you can use mini-muffin cups - just decrease baking time).
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In a large microwave-safe bowl, combine sugar, butter, and water. Microwave on high for 1 minute or until butter is melted.
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Stir in 3/4 cup semi-sweet chocolate chips until melted.
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Stir in egg and vanilla extract.
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Add flour and baking soda, stirring until blended. Allow to cool to room temperature.
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Stir in 1/2 cup each peanut butter chips and semi-sweet chocolate chips.
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Spoon batter by heaping tablespoonfuls into muffin cups.
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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.
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Place peanut butter in a small microwave-safe bowl. Microwave on high for 45 seconds, then stir.
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While brownies are still hot, spoon about a tablespoon of peanut butter into the center of each brownie. Top with remaining 1/3 c semi-sweet chocolate chips and 1/3 c peanut butter chips. Cool completely in pan, or eat warm with ice cream.