Cake layers:
7 large eggs, separated
3 large egg yolks
1 pound (3 1/2 cups or 455 grams) confectioners’ sugar, plus extra for dusting racks
3/4 cup (94 grams or 3 1/3 ounces) all-purpose flour
1 tablespoon lemon juice
1/8 teaspoon table salt

Frosting and filling:
1/2 pound (8 ounces or 227 grams) semi- or bittersweet chocolate, coarsely chopped
1/2 pound (2 sticks or 226 grams) unsalted butter, cut into chunks
1 teaspoon vanilla extract
3 large egg yolks
2 tablespoons confectioners’ sugar

Caramel layer (optional)
1/2 cup granulated sugar
1 tablespoon water
Handful of toasted, peeled hazelnuts