A delicious brownie that is healthier, but as good as it's fattier version. The secret is sweet potato and whole wheat flour, but no one will ever know... unless you tell them! I got this recipe from my Aunt.
Preheat oven to 350*F. Line an 8 inch square pan with enough foil to overlap the sides of the pan. Grease lightly and set aside.
Heat the margarine and chocolate morsels in a saucepan over medium heat until melted; remove from heat. Add sugar and beat until smooth. Stir in eggs, instant coffee and vanilla. Add the flour, sweet potatoe, cocoa powder, baking powder and salt; stir just until combined. Stir in the walnuts. (if using).
Spread the batter evenly into the pan. Bake for 25 minutes or until a toothpick comes out with only a few moist crumbs. Transfer to a cooling rack; let cool completely before slicing.