Preheat the oven to 180 degrees Celsius.
Line the brownie pan with baking paper to avoid the brownie from sticking to the pan. Leave an overhang of baking paper on either side – this makes it easy to lift the brownies from the pan.
Melt the chocolate and butter over a double boiler* until both ingredients are fully melted and combined.
113 grams white chocolate, 175 grams unsalted butter
Add the granulated sugar and brown sugar to the chocolate mix and stir it with a whisk until combined while it’s still hot.* The sugar will not dissolve completely, so don’t worry if the batter looks grainy at this point.
200 grams granulated white sugar, 125 grams brown sugar
Once the sugar is combined, add the eggs and vanilla extract, and whisk it again until the eggs are well incorporated into the chocolate batter, about 3-5 minutes.
3 eggs, 1 tsp vanilla extract
Add the all-purpose flour, salt, chopped pistachios and walnuts and fold them into the chocolate batter using a spatula or a wooden spoon. There should be no streaks of flour left in the batter by the time you’re done mixing it.
180 grams all-purpose flour, 1/2 tsp salt, 45 grams chopped pistachios, 45 grams chopped walnuts
Transfer the brownie batter to the prepared pan. Let it set at room temperature for 5-10 minutes; this will make the process of adding filo sheets easier.
Cut the filo pastry into strips and place one layer on top of the brownie batter. Brush it with melted butter then place another layer of filo pastry on top. Repeat for another layer, making sure the top is brushed with melted butter.
3 sheets store-bought filo pastry, 50 grams butter
Sprinkle the sugar on top evenly, then bake the brownie for 30-45 minutes, until the brownie is cooked through. For the last 5 minutes of baking, switch on only the top burner of the oven and bake until the filo pastry and sugar are caramelized, golden, and crispy. Keep an eye as it can burn very easily.
10 grams granulated white sugar
Let the brownies cool for at least 1 hour before slicing.