1. Preheat the oven to 325°F. Spray three 8-inch or two 9-inch cake pans with cooking spray and line with rounds of parchment.
2. In a medium bowl, whisk together the flour, coconut, baking powder, and salt.
3. In another medium bowl, whisk together the buttermilk, coconut oil, and vanilla.
4. In a stand mixer fitted with the paddle (or in a large bowl with an electric hand mixer), beat the butter and sugar together until extremely pale and fluffy, 4–5 minutes. Scrape down the sides and add the eggs, one at a time, beating well after each. Continue beating until the mixture is smooth, fluffy, and well incorporated, 2–3 minutes.
5. With the mixer on low, add about half the flour mixture, followed by the buttermilk mixture, followed by the remaining flour mixture (the idea being you don’t want to add too much liquid to the egg mixture or it’ll have a hard time incorporating, and you don’t want to overmix the flour, which will give you a tough cake).
6. Divide the batter evenly among the prepared pans and smooth the top. Bake until the cakes spring back lightly when touched at the top, look pale and blond on top and a nice golden brown on the sides, 30–35 minutes for the 9-inch and closer to 25–30 minutes for the 8-inch.
7. Let the cakes cool completely (either transfer them to a wire rack or let them cool in their pans), at least 1 hour at room temperature (do not rush the process by sticking them in the fridge).
8. If working with 9-inch cakes, use a long serrated knife to slice each one in half horizontally. It doesn’t have to be perfect, nobody will notice if it’s a little lopsided, I promise. If working with 8-inch cakes, you won’t have to slice anything, just proceed to the next step.
9. Lay one layer (either the halved 9-inch or the whole 8-inch) on a plate lined with parchment (or not). Spoon ⅓–½ cup (for the four-layer 9-inch or three-layer 8-inch, respectively) frosting onto the layer and use an offset spatula, spoon, or butter knife to spread it into an even layer. Top with another layer of cake. (Tip: If your cake is “domed” more than you’d like, invert it, so the flat side is facing up, not down, creating a flat top) and repeat with more frosting. Repeat until you’ve used all the cake layers.
10. Once you get to the top, spread a thin layer of frosting all over the cake (this is known as a “crumb coat”—think of it as a primer), making sure to get into the sides and crevices created during the slicing/layering. Pop the cake into the fridge to set for 30–60 minutes (but leave the rest of the frosting at room temperature).
11. Meanwhile, in a medium skillet, gently toast the coconut flakes over medium heat, tossing constantly, just until they are lightly toasted and golden brown at the edges, 2–3 minutes. (If you like your coconut more brown/toasted, then do it! I prefer just a kiss of toasting, but that’s personal preference.) Cool completely.
12. To finish the cake, spread the remaining frosting all over the sides and top of the cake. I want you to do the best you can, but also know you’re about to cover it all up with coconut, so don’t be too hard on yourself if it doesn’t look incredible. Pat the coconut onto the sides of the cake until evenly covered, using the rest to sprinkle on top.