For the Brownie Layer:

1. Preheat your oven to 350°F (175°C) and prepare a 9-by-13-inch metal baking dish by buttering it and lining with parchment paper.
2. In a small saucepan, melt the butter over low heat. Once melted, remove from heat and add the chopped bittersweet chocolate. Stir until the chocolate is completely melted. If needed, return to low heat briefly to help it melt fully. Set aside to cool slightly.
3. Sift together the flour, cocoa powder, and espresso powder (if using) in a small bowl.
4. In a medium mixing bowl, combine the eggs, both sugars, salt, and vanilla. Using a stand mixer with the whisk attachment or a hand mixer, beat on high speed for 4-5 minutes until the mixture becomes thick, pale, and falls from the beater in a ribbon that slowly dissolves.
5. Using a rubber spatula, gently fold the cooled chocolate mixture into the egg mixture.
6. Add the flour mixture and fold it in quickly but gently. Be careful not to deflate the air you’ve incorporated into the eggs.
7. Pour the batter into your prepared pan and smooth the top with a spatula.
8. Bake for about 25 minutes, until the top looks slightly cracked and feels soft to the touch.
9. Allow the brownies to cool completely on a wire rack before adding the next layer.

For the Pistachio Layer:

1. Take your kataifi pastry and chop it into 1/2-inch pieces, then separate the strands.
2. In a frying pan, melt 1 tablespoon of butter and add half of the chopped kataifi. Toast over medium heat for 5-10 minutes, stirring frequently to ensure it browns evenly. Repeat with the remaining butter and kataifi. Set aside to cool.
3. In a mixing bowl, combine the pistachio paste, tahini, melted coconut oil, and sea salt. Stir until well combined.
4. Fold in the toasted kataifi pastry until evenly distributed.
5. Spread this mixture in an even layer over the cooled brownies.

For the Chocolate Topping:

1. In a microwave-safe bowl, combine the chocolate chips and coconut oil.
2. Microwave in 30-second intervals, stirring between each, until completely melted and smooth.
3. Pour the melted chocolate over the pistachio layer and spread it evenly.
4. Place in the refrigerator (or leave at room temperature if your kitchen isn’t too warm) to set before cutting into squares.