1Spray a 9x13-inch baking pan with nonstick spray.
Combine the first 5 ingredients. In a mixer bowl beat together butter and shortening on medium speed of electric mixer about 30 seconds. Add sugar and vanilla and beat till well combined. Add eggs, one at a time, beating 1 minute after each. Add dry ingredients and buttermilk alternately to beaten mixture, beating on low speed after each addition. Pour into pan. Bake in a 350^ oven about 30 minutes or till dome. Just before cake is removed from oven, make the topping; quickly spread topping over hot cake, Sprinkle with coconut. Bake in a 350^ oven 5 minutes or till meringue is golden. Cool on a wire rack. Store in refrigerator.
Toasted Meringue Topping:
In a small bowl beat egg whites and vanilla on medium speed of mixer for 2 minutes or till soft peaks form Gradually add brown sugar, 1 Tablespoon at a time, beating on high speed for 4 minutes more or till mixture forms stiff, glossy peaks.