Combine ½ cup brown sugar and 1 cups flour in a medium mixing bowl; cut in butter with a pastry blender until mixture resembles coarse meal. Press dough evenly into a 8-inch square baking pan; bake at 375 degrees for 12 minutes. Set aside to cool.
Combine 1 cup of sugar, 1 teaspoon flour, salt, eggs, vanilla, coconut, and black walnuts in a medium mixing bowl. Pour over baked crust. Bake at 375 degrees for 22 minutes. Remove to a wire rack to cool. Cut into bars.