1 cup (250 mL) butter
4 squares unsweetened chocolate
2 cups (500 mL) granulated sugar
1 cup (250 mL) bean purée
2 tablespoons (30 mL) instant coffee
1 cup (250 mL) chopped walnuts
Grease a 13x9-inch (33x23 cm) baking pan. Line bottom and sides with a single sheet of parchment paper, leaving an overhang of 1 1/2 inches (4 cm) on the short sides, for easy removal.
In a double boiler, melt together butter and chocolate. Set aside.
Place sugar in the bowl of an electric mixer. Add eggs, one at a time, beating well after each addition. Add chocolate mixture and beat until well combined. Beat in bean purée and instant coffee. Use a spatula to fold in walnuts.
Pour mixture into baking pan and bake at 350°F (180°C) for 50 minutes for a moist, fudgy, creamy-textured brownie. If you prefer a drier brownie, bake an additional 5 to 10 minutes.
Cool completely on a wire rack before removing from pan. Loosen sides with a knife or thin metal spatula before lifting out onto a flat surface.
Cut with a sharp thin-bladed knife, which has been dipped in hot water and dried between cuts.
Yield is according to size. Cut into small squares for rich little cakes or into large squares, topped with ice cream, and serve for dessert. Cover with plastic wrap and store at room temperature for gooey brownies, or in the refrigerator for denser, fudgier brownies.