Tri-level brownies are triple delicious (1968)

Ingredients

• 1/2 cup sifted all-purpose flour
• 1/4 teaspoon baking soda
• 1/4 teaspoon salt
• 1 cup quick-cooking rolled oats
• 1/2 cup brown sugar
• 6 tablespoons butter or margarine, melted
• 1 ounce unsweetened chocolate, melted
• 4 tablespoons butter or margarine, melted
• 3/4 cup granulated sugar
• 1 egg
• 2/3 cup sifted all-purpose flour
• 1/4 teaspoon baking powder
• 1/4 cup milk
• 1/2 teaspoon vanilla
• 1/2 cup chopped walnuts
• 1 ounce unsweetened chocolate
• 2 tablespoons butter or margarine
• 1-1/2 cups sifted confectioners sugar
• 1 teaspoon vanilla