Pastry cream: in a saucepan, heat milk, cream, and half of the sugar over medium high heat and stirring gently until simmering. Separately, which together the remaining sugar, cornstarch and egg yolks. Once the milk mixture is hot, slowly whisk 1 cup of the mixture into the yolks to temper. Pour the tempered yolks into the milk mixture, reduce heat to medium and whisk and cook for ~30 seconds until thickened and a few bubbles appear.

Pastry cream: remove from heat and whisk in the butter, vanilla and almond extract. Transfer to a bowl, press a piece of plastic wrap against the surface to keep a skin from forming and refrigerate until firm ~3 hours.

Swiss buttercream: combine the egg whites and sugar in a bowl over a pan with simmering water; the water should not touch the bowl. Whisk until the water has dissolved and the temperature is 140-160 F. Transfer the mixture to a stand mixed and whip on high with the whisk attachment until thick and glossy with stiff peaks forming and the mixture temperature is room temperature (10-20 minutes).

Swiss buttercream: once the bowl is no longer warm to touch, decrease the speed to medium low and add the butter, 1 tablespoon at a time and beating until smooth. Once all of the butter has been added, mix the vanilla, almond extract, and salt.

Carmelized almonds: preheat the oven to 350 F and cover a baking sheet with parchment paper. Spread the nuts in an even layer and toast until light brown and smell nutty.

Carmelized almonds: while toasting the almonds, combine the water, sugar, lemon juice, and salt in a saucepan and heat over medium high heat until the sugar dissolved. Boil without stirring until 310 F and then remove from the heat and add the butter. Pour the mixture over the almonds in the pan and spread in a thin layer. Cool completely and then break apart large chunks.

Assemble: place a cake layer on a plate and pipe a border of Swiss buttercream around the edge to hold in the pastry area. Spread 1/3 of the pastry cream on the cake. Repeat with the other layers, topping with a cake layer with no pastry cream on top. Frost the cake with the Swiss buttercream. Before serving the cake, press the carmelized almonds on the top and sides of the cake.