Preheat your oven to 350°F (175°C) and prepare a baking dish by greasing it or lining it with parchment paper.
In a heatproof bowl, melt the dark chocolate and butter (or oil) together until smooth and well combined.
Allow the chocolate mixture to cool slightly before adding the eggs. Whisk in the eggs one at a time until fully incorporated.
Gradually mix in the powdered sugar until the mixture is smooth and glossy.
Sift together the all-purpose flour, cocoa powder, and a pinch of salt, then fold this dry mixture into the chocolate mixture until just combined.
Pour the brownie batter into the prepared baking dish and spread it evenly.
Bake in the preheated oven for about 20-25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Let the brownies cool in the pan before cutting them into squares and serving.
