For bottom layer, stir together oats, the 1/2 cup flour, the
brown sugar, and baking soda. Stir in the 1/2 cup melted butter. Pat
mixture into the bottom of an ungreased 11x7x1-1/2-inch baking pan. Bake
in a 350 degree F. oven for 10 minutes.
Meanwhile, for middle layer, stir together egg, granulated sugar,
the 2/3 cup flour, the milk, the 1/4 cup melted butter, 1 ounce melted
chocolate, the 1 teaspoon vanilla, and the baking powder until smooth.
Fold in chopped walnuts. Spread batter over baked layer in pan. Bake
about 25 minutes more or until a wooden toothpick inserted in center
comes out clean. Set on a wire rack while preparing top layer.
For top layer, in a medium saucepan heat and stir 1 ounce
chocolate and the 2 tablespoons butter 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 almost pourable. Spread over
brownies. If desired, garnish with walnut halves. Cool completely on
wire rack. Cut into bars. Makes 32 brownies.