Walnuts:

Cup of Yum
1. Roast walnuts: Preheat the oven to 220°C/ 430°F. Line the baking sheet with parchment paper. Spread the walnuts on it in an even layer and roast for about 3 or 4 minutes until slightly golden and beginning to be fragrant. Keep an eye on them; they should not get too dark, or they will taste bitter. Remove them from the oven and let them cool completely.350 g shelled walnut halves/ 12.5 oz
2. Grind: When cold, grind them finely either in the food processor or place them in a large freezer bag and crush them with the rolling pin. Set aside.

Caramel:

1. Weigh 100 g/ 3.5 oz/ 1 cup of the roasted and ground walnuts and set them aside.
2. Make the caramel: Place a sheet of aluminum foil on a large plate and set it aside. Place sugar in a non-stick pan. Let it caramelize, taking care that it doesn't get too dark. Next, take off the heat and stir in the walnuts you have just weighed.5 tablespoons granulated sugar + just weighed walnuts (100 g/ 3.5 oz)
3. Cool: Spread this mixture on the aluminum foil and let it set completely.

Cake base:

1. Preheat the oven to 180°C/ 350°F. Line the baking sheet with parchment paper.
2. Make the batter: Separate the eggs. Set the yolks aside; you will only need them for the buttercream. Beat the egg whites with a pinch of salt until stiff. Add 3 tablespoons sugar, rum (optional), and lemon juice and continue beating until stiff and glossy. Carefully fold in the rest of the ground and roasted walnuts.8 eggsegg whites + 1 pinch of salt + 3 tablespoons granulated sugar + 1 tablespoon rum + 2 tablespoons lemon juice + remaining ground walnuts
3. Bake: Pour this mixture onto the prepared baking tray and bake the cake base for about 20-25 minutes. Let it cool completely, then slice it into 3 equal rectangular parts.

Buttercream:

1. Mixture: Beat the egg yolks with 9 tablespoons of sugar until pale and creamy. Slowly add the milk and incorporate it. Pour the mixture into a saucepan and place it on a very low flame. Stir continuously with a wooden spoon until the mixture thickens; it took me 15 minutes on a very low flame. Set aside, place a piece of plastic foil on top to prevent it from getting skin, and let it get completely cool.egg yolks + 9 tablespoons granulated sugar + 200 ml milk/ ¾ cup + 2 tablespoons
2. Make the buttercream: In the meantime, take the butter out of the fridge and let it soften. Beat the soft butter with the hand-held mixer until light and fluffy. Start adding the cold egg yolk cream, one tablespoon at a time, while beating continuously. Beat in the vanilla extract to taste, as well.300 g unsalted butter/ 10.5 oz/ 1 ¼cups + 1 tablespoon + 1-2 teaspoons vanilla extract

Assemble:

1. Fill cake: Place one slice of the cake base on a rectangular serving platter. Cover with one-third of the buttercream, place another piece of cake on top, cover with another third of the buttercream. Finally, place the third cake slice on top and cover with the rest of the buttercream.
2. Top: Roughly crush the caramelized walnuts and top the cake with them. Let rest in the fridge overnight.