How to Make It
Preheat the oven to 325°. Butter three 9-inch round cake pans. Line the bottoms with parchment paper; butter the paper and flour the pans. In a large bowl, whisk the flour, baking powder and salt. In a standing electric mixer fitted with a paddle attachment, beat the butter and sugar at medium speed until light and fluffy. Beat in the vanilla. At low speed, beat in the dry ingredients and the milk in 3 alternating batches; be sure to scrape the side and bottom of the bowl.
In a clean bowl, beat the egg whites to soft peaks. Beat one-third of the egg whites into the batter. Using a rubber spatula, fold in the remaining beaten whites until combined. Divide the batter between the prepared pans. Bake for 25 to 30 minutes, until the cakes are lightly golden and springy. Let the cakes cool in the pans for a few minutes, then invert them onto racks to cool completely. Peel off the parchment paper.
Spread the pecans on a baking sheet and toast for 10 minutes, until fragrant. Let cool, then coarsely chop. In a medium saucepan, melt the butter over low heat. Remove from the heat and whisk in the egg yolks and sugar until smooth. Return the pan to moderate heat and cook the filling, stirring constantly, until slightly thickened and an instant-read thermometer reads 180°; be sure not to let it boil. Remove from the heat and stir in the chopped pecans, coconut, raisins and bourbon. Transfer to a bowl and let cool.
In a medium bowl, beat the butter until creamy. Add the vanilla and salt, then gradually beat in the confectioners' sugar, being sure to scrape the side and bottom of the bowl. Add the half-and-half and beat until fluffy, about 1 minute.
Place a cake layer on a plate and top with one-third of the filling, spreading it almost to the edge. Top with a second cake layer and another third of the filling. Top with the last cake layer. Using an offset spatula, spread a thin layer of the buttercream all around the cake, being sure to fill in any gaps between the layers. Refrigerate the cake for 10 minutes, to firm up the buttercream.
Spread the remaining buttercream around the side of the cake only, leaving the top with just the thin layer of buttercream. Spread the remaining filling over the top of the cake. Let the cake stand for at least 4 hours before cutting.