Preheat the oven to 170°C. Line a 20 cm round cake pan with parchment paper and lightly grease it.

Melt the chocolate and butter together over a double boiler or in a microwave-safe bowl (using short bursts), stirring until smooth. Set aside to cool slightly.

Separate the eggs in different bowls

In a large bowl, beat the egg whites, sugar, and vanilla extract until stiff peaks form .

Add the egg yolks to the melted chocolate and butter mixture – mix well.

Add the sifted flour and cocoa powder, stirring until combined. The mixture will be thick.

Add all the whipped egg whites to the chocolate mixture at once. Gently fold using a spatula: start from the bottom, lift the chocolate mixture over the whites, and turn the bowl as you go.

Continue folding slowly until no white streaks remain—do not overmix to keep it airy and fluffy.

Pour the batter into the prepared pan and smooth the top. Bake for 25-30 minutes, or until the top is set, the edges are slightly firm, and the center is still soft and fudgy. A toothpick inserted should come out with moist crumbs (not wet batter).

Cool completely in the pan before unmolding.