• Preheat oven to 200°C (400°F).

For the chocolate brownie

• In a bowl pour the flour, almond powder, sugar and pinch of salt. Mix well.
• Melt the chocolate with the butter (in a double boiler or in the microwave).
• Pour melted chocolate/butter over dry ingredients mixture. Stir to combine.
• Add the eggs, one by one, mixing well between each.
• Set aside at room temperature while you make the pistachio brownie.

For the pistachio brownie

• In a bowl pour the flour, almond powder, sugar and pinch of salt. Mix well.
• Melt the butter.
• Gradually pour the melted butter over the pistachio paste, mixing well between each addition. You should obtain a liquid paste.
• Pour it over the dry ingredients mixture. Stir to combine.
• Add the eggs, one by one, mixing well between each.
• Add the roughly chopped pistachios, keeping 1 tablespoon for decoration.
• In a buttered and floured dish (or lined with parchment paper), pour alternating strips of chocolate and pistachio dough vertically (for more precision you can transfer your dough into pastry bags). To create the marbled effect, use the tip of a knife to make lines in the opposite direction of the strips (i.e. horizontally, see the video in the text above).
• Sprinkle with remaining chopped pistachios.
• Bake for about 25 minutes, the brownie should still be "sticky" in the center (it should not be overcooked).
• Allow to cool before unmolding, then cut into 9 squares.