Vanilla and Chocolate Conchas

Name: Vanilla and Chocolate Conchas
Prep time: 60 min
Yield: 5
Cuisine: Mexicana
Ingredients: 2 1/2 cups flour; 4 eggs; 1 cup sugar; 3/4 cups margarine; 4 tablespoons yeast; 1/2 cups water; 1/2 cups cow's milk; 3/4 cups wheat flour, for the layer; 3/4 cups icing sugar, for the layer; 1/2 cups vegetable shortening, for the layer; 1 egg white, for the layer; 1 teaspoon vanilla essence, for the layer; 1 stick chocolate, melted, for the layer