Preheat oven to 180°C (350°F)
Start by melting 200g of dark chocolate and 125g of butter together. You can do this in the microwave in short increments, stirring frequently, or over a bain-marie (double boiler). Stir until the chocolate and butter are completely smooth and melted.
In a separate bowl, crack 3 eggs and add 100g of sugar. Using a hand mixer or whisk, beat the eggs and sugar together until the mixture becomes light and fluffy and doubles in volume.
Once the egg mixture is ready, slowly pour in the melted chocolate and butter. Mix until the chocolate is fully incorporated into the eggs.
Add 100g of flour to the mixture, folding it in gently. Mix until there are no lumps, and the batter is smooth and glossy.
Pour the brownie batter into a prepared baking mould. Bake in the preheated oven for 20 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (this will ensure a fudgy texture).
Allow the brownies to cool before cutting them into squares.