Directions

1. Make the cake: Heat the oven to 350° F. Butter and lightly flour three 9-inch cake pans, tapping out any excess flour. In a heavy-bottomed saucepan, melt the butter. Cook over medium to low heat, stirring once in a while until foamy, then continue to cook, stirring frequently, until you are seeing small brown bits in the butter and it smells nutty. This whole process takes 10 to 15 minutes. Scrape your butter and any browned bits into the bowl of your stand mixer, then put that bowl into an ice bath in the fridge. Let sit for about 10 minutes, until the butter along the outside of the bowl starts to set and turn opaque. Meanwhile, whisk together the flour, baking powder, and salt. Put the bowl with the butter (once ready) onto the mixer, and beat until creamy. Add the sugar and beat until light and fluffy. Then add the egg yolks, beating to combine, followed by the whole eggs, beating to combine again, then the vanilla. Beat in the dry ingredients and buttermilk in 3 alternating additions, scraping down the bowl as necessary. Pour the batter evenly into the 3 prepared pans and bake, rotating the pans once while baking, for about 30 minutes. A toothpick or cake tester should come out clean, or with a couple dry crumbs. Cool the cakes in the pans for 15 minutes, then turn out and allow them to cool completely on racks while you work on the rest of the trifle. Once cool, chop the cake up into 1 to 2-inch square pieces.
2. Pastry cream: Heat the milk, vanilla seeds and pod, and salt in a pan and put over medium heat. Bring to a boil. Meanwhile, heat a small saucepan with some water to a boil. In a large mixing bowl, whisk the sugar, cornstarch, and eggs until smooth. Don't let these items sit together because the sugar can "cook" the yolks and make them grainy. Slowly add 1/2 of the milk mixture into the egg mixture and whisk constantly to temper them. Add the remaining milk. Place this bowl over the saucepan of boiling water. Whisk constantly until you get a thick consistency and the mixture registers 180° F, about 10 to 12 minutes. Remove from heat and let cool for about 10 minutes, until it registers 140° F, and then incorporate the butter, one tablespoon at a time, until smooth. Cover the surface with plastic wrap, directly touching the cream. Let cool completely in the fridge.
3. Fruit purée: Purée the mango purée, lime juice, lime zest, and 1/2 cup sugar in a blender or food processor. Add the Champagne to taste, if using. Set aside.
4. Assembly: Whip the whipping cream and tablespoon of sugar in a mixer until it holds medium peaks. Then begin putting the trifle together... Begin with 1 pan's worth of the cut up cake squares, scattered along the bottom of your trifle dish. Cover the cake with 1/3 of your fruit purée, then 1/3 of your mango (and raspberries, if using), 1/3 of the toasted coconut, 1/3 of the pastry cream, and finally 1/3 of the whipped cream. Repeat 2 more times. Smooth out the top of your last layer of whipped cream. The trifle can keep, in the fridge, for a day, and I prefer to wait at least a couple hours before serving so the fruit purée cake seep into the cake a little.