How to Make It
Preheat the oven to 350° and position 2 racks in the middle and lower thirds. Line the bottoms of three 9-inch round cake pans with parchment or wax paper. In a medium bowl, whisk the cake and all-purpose flours with the baking powder and salt. Combine the milk and vanilla in a small pitcher.
In a large bowl, using an electric mixer, beat the butter at medium speed until creamy. Add the sugar and beat until the mixture resembles moist sand, about 3 minutes. Beat in the flour mixture at low speed in 3 batches, alternating with the milk mixture; stop the mixer occasionally to scrape down the bowl. Add the eggs, 1 at a time, beating at medium speed between additions.
Divide the batter evenly among the cake pans. Bake for about 25 minutes, or until the layers are light golden and a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then turn each out onto a rack and peel off the paper. Invert onto another rack and let cool completely.
Center a cake layer on a platter and spread one-third of the Coconut Pecan Filling over the top, leaving a 1/2 -inch border at the edge. Set a second cake layer on top of the first and spread another third of the filling on top. Cover with the third cake layer. Spread the top and side of the cake with the Chocolate Frosting. Spread the remaining Coconut Pecan Filling over the frosting on the top, leaving a 1-inch border.