Preheat oven to 350º F. Grease three 9-inch round cake pans.

Using an electric mixer, cream together butter and shortening until light and fluffy.  Add sugar one cup at a time, making sure to fully incorporate each cup before adding another. Do the same with the eggs. Add the lemon zest.

Sift together flour, baking powder, and salt. Pour milks, lemon juice, and vanilla into measuring cup and whisk together with a fork. Add to butter mixture alternately with milk mixture, beginning and ending with dry ingredients.

Gently stir all ingredients until well combined. Scrape down bowl to be sure.

Distribute in the pans and  bake for 25-30 minutes until tester comes out clean. Remove and allow to cool completely before frosting.

While cake is cooling make frosting.

In the bowl of an electric mixer, using a handheld whisk, beat together the egg whites, sugar, corn syrup and salt just until combined, about 30 seconds. Place the bowl over but not touching simmering water in a saucepan and whisk until the sugar dissolves and the mixture is hot, 2 to 3 minutes.

Set the bowl on the mixer fitted with the whisk attachment and beat on medium speed for 3 minutes. Add the vanilla and beat until the outside of the bowl is cool and stiff peaks form 5 to 7 minutes more. Using a rubber spatula, fold in the coconut just until incorporated. Frost cake and use a kitchen torch to brown however you want.