Prep the pans and oven: Heat oven to 350°F (175°C). Grease and flour three 8-inch round cake pans or line bottoms with parchment.
This helps the delicate layers release cleanly.
Whisk dry ingredients: In a medium bowl, whisk flour, baking powder, and salt. Set aside to keep the batter lump-free.
Cream butter and sugar: In a large bowl, beat butter and granulated sugar on medium-high until pale and fluffy, about 3 minutes. This step traps air for lift.
Add egg whites and vanilla: Beat in egg whites one at a time, scraping the bowl.
Mix in vanilla. The batter will look silky and thick.
Alternate flour and milk: On low speed, add the dry ingredients in three parts, alternating with milk in two parts. Start and end with flour.
Mix just until combined to avoid a tough cake.
Divide and bake: Evenly divide batter among pans. Smooth tops and bake 20–24 minutes, until a toothpick comes out clean and edges are lightly golden. Cool in pans 10 minutes, then turn out onto racks to cool completely.
Make the filling: In a saucepan over medium-low, whisk egg yolks, sugar, butter, evaporated milk, vanilla, and salt.
Stir constantly until thick enough to coat a spoon, about 6–8 minutes. Remove from heat, stir in bourbon, pecans, coconut, and dried fruit. Cool to room temp; it will thicken more as it cools.
Prepare the frosting: Beat butter until creamy.
Add powdered sugar gradually, alternating with cream, until fluffy and spreadable. Beat in vanilla and salt. Adjust texture with more sugar (thicker) or cream (looser).
Assemble the cake: Place first layer on a plate.
Spread half the filling evenly, leaving a small 1/2-inch border to prevent spillover. Add second layer and spread remaining filling. Top with third layer.
Crumb coat and chill: Spread a thin layer of frosting over the top and sides to seal in crumbs.
Chill 20–30 minutes so the frosting sets.
Finish frosting: Apply a final smooth coat of frosting. Garnish with toasted coconut and pecans if you like. For tidier slices, chill the cake 20 minutes before cutting.