1 cup quick-cooking rolled oats
1/2 cup all-purpose flour
1/2 cup packed brown sugar
1/4 teaspoon baking soda
1/2 cup butter, melted
3/4 cup granulated sugar
2/3 cup all-purpose flour
1/4 cup milk
1/4 cup butter, melted
1 ounce unsweetened chocolate, melted and cooled
1 teaspoon vanilla
1/4 teaspoon baking powder
1/2 cup chopped walnuts
1 ounce unsweetened chocolate
2 tablespoons butter
1 1/2 cups sifted powdered sugar
1/2 teaspoon vanilla
1. Preheat oven to 350 F. For the bottom layer: In a small bowl, stir together oats, the 1/2 cup flour, the brown sugar, and baking soda. Stir in the 1/2 cup melted butter. Pat the mixture into the bottom of an ungreased 1171 1/2-inch baking pan. Bake for 10 minutes.
2. Meanwhile, for the middle layer: In a medium bowl, beat egg with a fork; stir in granulated sugar, the 2/3 cup flour, the milk, the 1/4 cup melted butter, the 1 ounce melted chocolate, the 1 teaspoon vanilla, and the baking powder until smooth. Fold in chopped walnuts. Spread batter evenly over baked layer in pan. Bake about 25 minutes more or until a toothpick inserted in center comes out clean. Place on a wire rack while preparing top layer.
3. For the top layer: In a medium saucepan, combine 1 ounce chocolate and the 2 tablespoons butter; heat and stir over low heat until melted. Stir in the powdered sugar and the 1/2 teaspoon vanilla. Stir in enough hot water (1 to 2 tablespoons) to make a mixture that is spreading consistency. Spread over brownies. Garnish with walnut halves. Cool in pan on a wire rack. Cut into bars.
Recipe shared from: http://www.bhg.com/recipe/brownies/trilevel-brownies/