1

Preheat oven to 350 ºF. Coat two 9-inch round or square cake pans with cooking spray; set aside.

2

To make the cake, combine flour, brown sugar, cocoa, baking powder, baking soda and salt in a large bowl. Mix well with a fork to break up brown sugar; set aside.

3

Melt 4 tablespoons of margarine. Combine buttermilk, egg whites, melted margarine and 1 1/2 teaspoons of vanilla extract in a large mixing bowl; using an electric mixer, mix on low speed until blended. Gradually beat in boiling water and then add flour mixture; mix on low speed until blended.

4

Pour batter into prepared pans and bake until a toothpick inserted in the centre comes out clean, about 30 minutes. Cool cakes in pans on a wire rack for 20 minutes; invert cakes onto rack, remove pans and cool completely.

5

Meanwhile, to make the frosting, melt remaining 2 tablespoons of margarine in a small saucepan over medium-low heat. Add milk and chocolate chips; cook until blended and smooth, stirring constantly with a wire whisk, about 3 minutes. Remove from heat, transfer to a large mixing bowl and stir in remaining 1/2 teaspoon of vanilla extract; cover surface with plastic wrap and refrigerate until cool, about 15 minutes. Using an electric mixer on low speed, gradually add powdered sugar and mix until blended.

6

To assemble cake, spread 1/2 cup of frosting on the top of one cake layer. Top with second cake layer and spread remaining frosting over top and sides; slice into 16 pieces and serve.