Step 1

Preheat oven to 325 degrees. Butter an 8-inch square baking dish. Line bottom with parchment paper, allowing 2 inches to hang over 2 sides. Butter parchment; set aside. Melt butter and chocolate together in a medium saucepan over medium-low heat, stirring until smooth. Remove from heat, and stir in remaining ingredients.

Step 2

Pour batter into prepared dish. Smooth top with a rubber spatula. Bake until a cake tester inserted into center comes out with moist crumbs, 30 to 35 minutes. Let cool in pan on a wire rack 15 minutes. Lift out, and let cool completely on rack. Cut into sixteen 2-inch squares.