• Preheat oven to 350ºF / 180ºC. Line a 13x9 inch (33x23 cm) baking pan with foil that hangs down the two long sides, or butter and flour it.

For the blondie layer:

• In a bowl mix the melted butter, sugar, egg, egg white and vanilla until well blended.
• Sift the flour, baking powder and salt directly on top of the mixture and mix until no dry spots remain. Drop the blondie thick batter by tablespoons onto the pan.
• Carefully spread the mixture, trying to get an even layer. Don´t become too obsessed with it though. Sprinkle the nuts on top.
• Bake for about 20 minutes, until it´s no longer shiny on top. This is only a partial bake, so don´t let it bake completely and dry out.
• Transfer to a wire rack while you make the brownie layer.

For the brownie layer:

• Melt chocolate and butter together, either in the microwave (at 30 second intevals, stirring well between each. It should take a minute or so to melt), or on top of a double boiler without letting the bottom of the pan touch the water. Transfer chocolate mix to a bow and let cool a few minutes.
• Add sugar and mix well with a spatula. Add eggs, egg yolk, vanilla and mix until smooth. Don´t beat the batter.
• Finally add the flour, cocoa, baking powder and salt, sifting it directly on top of the chocolate batter. (You can sift all dry ingredients before onto a piece of wax paper or a bowl too, and then just add them without sifting again). Mix well with the spatula.
• Spread evenly on top of the blondie layer. To do this, drop the thick batter in tablespoons all through the surface, then spread carefully with the back of a spoon or a spatula. The warm blondie layer will help the spreading a bit.
• Bake for about 25 minutes, until it´s dry on top and a tester comes out with moist (but not wet) crumbs attached. Don´t let it dry or the bars will be tough.
• Let cool on a wire rack. Unmold, drizzle with dulce de leche or caramel and serve.

For the glaze:

• Heat dulce de leche or caramel with the cream in a small saucepan, until it becomes thinner.