Key Lime Coconut Cake with Marshmallow Frosting
Billowy frosting cloaks a moist and buttery lime-flecked cake whose subtle coconut flavor comes from canned cream of coconut.
Stir the cream of coconut in the can before measuring.
In the top of a double boiler combine 1 1/2 cups sugar, 1/3 cup cold water, 2 egg whites, and 1/4 teaspoon cream of tartar. Beat with an electric mixer on low speed for 30 seconds. Place over boiling water (upper pan should not touch water). Cook, beating constantly with the electric mixer on high speed, about 10 minutes or until frosting forms stiff peaks (tips stand straight) and mixture reaches 145°F for 3 minutes or 160°F for 15 seconds when tested with an instant read thermometer. Scrape pan occasionally. Remove from the heat; add 1 teaspoon vanilla. Beat 2 to 3 minutes more or until frosting reaches spreading consistency.