Ingredients

• 1 stick (1/2 cup) unsalted butter, cut into pieces
• 2 ounces unsweetened chocolate, chopped
• 1 1/2 cups mint chocolate chips (about 12 ounces)
• 1 cup sugar
• 1/2 teaspoon vanilla
• 2 large eggs
• 2/3 cup all-purpose flour
• 1/2 teaspoon salt

Instructions

1. Preheat oven to 350°F. and butter and flour a 9-inch square baking pan, knocking out excess flour.
2. In a heavy 1 1/2-quart saucepan melt butter, unsweetened chocolate, and 1/2 cup mint chocolate chips over low heat, stirring, until smooth and remove pan from heat. Cool mixture 10 minutes and stir in sugar and vanilla. Add eggs, 1 at a time, beating well with a wooden spoon until mixture is glossy and smooth. Stir in flour, salt, and remaining cup chocolate chips until just combined.
3. Spread batter evenly in pan and bake in middle of oven 25 to 30 minutes, or until a tester comes out with crumbs adhering to it. Cool brownies completely in pan on a rack before cutting into thirty-two 2- by 1-inch bars. Brownies keep, layered between sheets of wax paper in an airtight container at cool room temperature, 5 days.