1 3/4 cups boiling water
1/2 cup unsalted butter
1/2 cup white sugar
1 cup brown sugar
3/4 cup all-purpose flour
1 teaspoon salt
3 tablespoons unsalted butter, softened
1 teaspoon baking soda
1 1/2 pounds large cake mix
2 egg whites
1 cup white sugar
1/2 teaspoon vanilla extract
In a large bowl, combine boiling water, 1/2 cup butter and 1/2 cup sugar. Cook over a double boiler until mixture thickens; stir in brown sugar. Remove from heat and stir in flour, salt, and 3 tablespoons of butter. In a small bowl, cream together egg white and 1 cup sugar. Roll out cake mix and pour into prepared pan.
Preheat oven to 400 degrees F (200 degrees C).
Bake in preheated oven for 25 to 30 minutes, or until a toothpick inserted into the cake comes out clean. When cool, stir in the vanilla and 1 cup of white sugar. Cool completely before icing.