Prepare two 9-inch round baking tins by covering the bottom with a circle of wax paper.
In a mixing bowl, whisk the eggs, the yolk and the sugar to the ribbon stage. Fold in the flour and ground walnuts.
Meanwhile, make the meringue by whisking the egg whites on high speed until fluffy. Add a pinch of salt and the vanilla. Change to low speed and sprinkle in the sugar. Whisk on high speed for 5 minutes until you obtain a firm, glossy meringue.
Carefully add one-third of the meringue to the walnut and egg mixture. Slowly fold in the remaining two-thirds to prevent the mixture from deflating.
Divide mixture between the prepared baking tins. Bake for 12 to 15 minutes until the cakes are dry to the touch and golden on the surface. Allow cakes to cool, then remove from the baking tins.
Place a little dulce de leche on the plate where the cake will be assembled. Add the first sponge cake and cover with a layer of dulce de leche and sprinkle with chopped walnuts. Top with the second cake, then covering the whole cake with dulce de leche and walnuts.