Take off the top part of the angel food cake and scoop out some of the cake making a trench. Fill with mousse then replace the top layer of cake. In a small sauce pan melt butter and remove from heat. Sift in sugar and stir in Grand Marnier until combined well. Heat mixture over moderate heat, stiriing, until it just begins to bubble. Remove pan from heat and stir in almonds. Immediately pour everly over cake, allowing it to drip down sides and chill cake 15 minutes before serving.