Heat oven to 350 degrees. Grease and flour 15 x 10 x 1 pan. In large bowl, mix the cake mix, 1/2 cup butter, sour cream, and eggs at low speed, then two minutes at high. Stir in nuts. Spread in pan. Bake at 350 degrees for 18 to 20 minutes till center is firm. In medium bowl, combine coconut and milk. Spoon and spread over base. Return to oven. Bake 15 to 20 minutes until golden brown. Cool completely, then frost with your favorite chocolate frosting. This is great!