In a bowl place 4 tablespoons of butter or margarine, 1 1/4 cup of sugar and beat until light and creamy.
Add 1/2 cup of cream, wheat flour, milk, vanilla sugar and beat until smooth and homogeneous.
Add the baking powder and mix gently just until incorporated.
Grease a rectangular shape with butter or margarine, pour all the dough and bake in a preheated oven at 200°C for 35 minutes.
For the frosting, in a pan put 1/2 cup of sugar and bring to the fire stirring constantly until melted and caramelized. Add 1 tablespoon of butter and mix.
Add 1/2 cup of cream, condensed milk and stir until it thickens and releases from the bottom of the pan.
Remove the cake from the oven, cover with the dulce de leche, cut into pieces, decorate each piece with a walnut and serve.