1. Preheat oven to 350° F (175° C). Spray a 9x13 inch (23x33 cm) baking pan with non-stick spray.
2. Melt margarine and chocolate in a double boiler or microwave.
3. Mix egg yolks and then slowly stir them into the chocolate. Make sure the yokes do not harden.
4. Let the chocolate-egg mixture cool.
5. Whip egg whites until stiff. Add sugar.
6. Add egg whites to chocolate mixture, folding gently.
7. Remove 1 - 1 1/2 cup of the mousse mixture. This will be used later for the cake's frosting.
8. Gently add flour to the rest of the mixture.
9. Pour mixture into baking pan. Bake for 35-40 minutes.
10. When cool, spread frosting on top. Refrigerate or freeze.
TIPS:
1. If using the microwave to melt the chocolate and margarine, be careful not to burn the chocolate.
2. Don't forget to add the flour between removing some mix for the frosting and putting the pan into the oven!