Mint Chocolate Brownies

I just tried this one out today and it's pretty good. I found it on this site, and altered the pan and cooking time because I like my brownies to be thicker and fudgier than the original recipe would have given me :)
2/3 cup butter OR margarine

1 2/3 cups (10-ounce package) HERSHEY'S Mint Chocolate Chips, divided

1 1/2 cups granulated sugar

1 cup all-purpose flour

1/3 cup HERSHEY'S Cocoa

1 teaspoon vanilla extract

1/2 teaspoon baking powder

1/2 teaspoon salt

3 large eggs

1 cup coarsely chopped walnuts (optional)


Heat oven to 350°F. Grease 8x8-inch baking pan.
Place butter and 1 cup mint chocolate chips in large microwave-safe bowl. Microwave at 20-sec intervals, stirring in between, until chips are melted.
Add sugar, flour, cocoa, vanilla, baking powder, salt and eggs; stir with spoon until smooth. Stir in remaining 2/3 cup chips. Spread batter into prepared pan; sprinkle walnuts over top.
Bake 25 minutes or until center is set. Cool completely in pan on wire rack. Cut into bars.