Preheat oven to 350 degrees with rack in middle of the oven. Grease and line with parchment two 9×3-inch Cake Pans. In a medium bowl whisk together the flour, baking powder and salt, set aside.
Mix the coconut milk and vanilla, set aside.
In a stand mixer fitted with a paddle attachment, beat the butter and sugar on medium-high speed until light and fluffy, about 4 minutes. (Scrape down the bowl if you don’t have a beater blade) Add the eggs one at a time and beat well after each addition.
Add 1/3 of the flour mixture and mix on low speed until incorporated. Add half the coconut milk and mix thoroughly. Continue to add the flour and coconut alternately, ending with flour. Add sour cream and mix until incorporated. Set aside in a large bowl if you don’t have a spare bowl for your mixer.
Beat the egg whites in your stand mixer with the whisk attachment. (If you are using the same Bowl be sure it is VERY CLEAN or the whites will not whip up. Any fat on the bowl will prevent the whites from foaming.) Beat the whites on high speed for 2-3 minutes, until it forms soft peaks. Don’t overdo it or the whites will get too stiff and not fold into the batter smoothly. Whites beaten without sugar will get too stiff quickly so check them after 2 minutes.
Stir 1/3 of the egg whites into the cake batter to lighten it. Gently fold the remaining whites into the batter.
Divide evenly in the prepared pans. Bake for about 25-30 minutes or until the tester comes out clean. Cool on rack in pan and then invert to use.