Preheat oven to 350 degrees..

Spray or butter three 8-inch cake pans and dust with flour.

1. In a medium bowl, combine the flour, baking powder, baking soda and salt.
2. In a large bowl, use an electric mixer to beat the sugar, butter and coconut milk until fluffy.
3. Beat in the egg yolks and vanilla extract.
4. On low speed, add the dry ingredients followed by the buttermilk, mixing just until blended.
5. In a separate bowl, beat the egg whites with a pinch of salt until stiff but not dry.
6. Gently fold the beaten egg whites into the batter.
7. Spoon the batter into prepared pans. Bake until a tester inserted in the center comes out clean, about 45 minutes. Cool cakes in the pans on a rack for 10 minutes. Turn cakes out onto racks and cool completely.
8. While the cakes are cooling, prepare the filling: combine the sugar, sour cream and milk in a small bowl.
9. To assemble the cake, place 1 layer on a cake plate and poke several holes in the cake using a fork or skewer. Spread half of filling mixture over the cake and sprinkle with 1/4 cup coconut. Top with the second layer and repeat. Finally, top with the third layer.
10. Refrigerate until ready to frost.
11. Frost with 7-minute frosting and sprinkle generously with toasted coconut.
12. Refrigerate completed cake. Remove from refrigerator 1–2 hours before serving.