Beat the eggs with the powdered sugar until you get a fluffy cream and they soften. Add the flour, sifted with the baking powder, the ground walnuts and carefully mix. Pour the mixture into a buttered cake form and bake in a moderately preheated oven.
Put the crystal sugar in a pan, pour in 1 cup water and caramelize it on the stove. Once you've obtained the caramel, add 1 cup boiling water and stir nonstop until the caramel dissolves in the water, then remove from the stove immediately.
Invert the cooled walnut cake layer onto a deep plate. Slowly pour the hot caramel evenly over the cake. Pour the caramel that spills down the sides of the layer on top as well, until the cake gets soaked nicely.
Invert the syruped walnut cake into a serving plate. Beat the egg white with the powdered sugar and a little lemon juice and make a decoration on top.