Romanian Walnut Buttercream Cake

Walnuts:
Preheat oven to 220 degrees Celsius/ 430 degrees Fahrenheit. Line a baking tray with baking paper, spread the walnuts evenly, and roast for 3-4 minutes until slightly golden. Let cool, then grind finely.
Caramel:
Set aside 100 g of ground walnuts. Make caramel by heating sugar in a non-stick pan until it caramelizes lightly, stir in the walnuts, spread on foil, and let set.
Cake Base:
Preheat oven to 180 degrees Celsius/ 350 degrees Fahrenheit. Beat egg whites with salt to stiff peaks, incorporate sugar, rum, and lemon juice. Fold in ground walnuts, bake the mixture in a lined tray for 20-25 minutes, then let cool and slice into 3 parts.
Buttercream:
Beat egg yolks with sugar until pale, add milk, and cook until thick. Let cool. Beat butter until fluffy, gradually add yolk mixture, and vanilla.
Assemble:
Layer cake slices with buttercream, top with crushed caramelized walnuts. Refrigerate overnight.
Prep Time: 1 hour | Cooking Time: 1 hour | Total Time: 2 hours | Kcal: 516 | Servings: 10-12