Heat oven to 350°F. Grease bottom only of 13x9-inch pan with shortening or cooking spray. In food processor, place 1/3 cup of the almonds. Cover and process, using quick on-and-off motions, until almonds are ground. Chop remaining almonds; set aside.
In 3-quart saucepan, melt chocolate and 1/3 cup butter over low heat, stirring frequently, until smooth; remove from heat. Stir in ground almonds, flour, granulated sugar, baking powder, salt, 2 tablespoons amaretto and the eggs. In pan, spread batter evenly.
Bake 22 to 27 minutes or until toothpick inserted in center comes out clean. Cool completely.
In medium bowl, mix all frosting ingredients until smooth and spreadable. Spread frosting over brownies. Sprinkle with chopped almonds. For brownies, cut into 8 rows by 4 rows.