Grease and flour two 20 cm or 23 cm round cake pans. In large bowl, blend all cake ingredients, except nuts, until moistened. Beat 2 minutes at high speed; fold in nuts. Pour batter into prepared pans. Bake 23 cm layers for 30-40 minutes; 20 cm layers for 35-45 minutes, at 160ºC Cool 15 minutes in pans; loosen sides and remove from pans. Cool completely. In a small bowl, dissolve drink mix and instant coffee in hot water. Add powdered sugar, Bit's of Brickle and margarine; beat until fluffy. Slice cooled cake into 4 layers; gently spread one third filling between each layer. Frosting: In small bowl, combine Cool Whip and powdered sugar. Frost top and sides of cake. Garnish cake with whole or halves walnuts. Refrigerate cake for at least 2 hours.