Melt the chocolate: Break the chocolate into small pieces and melt using a double boiler or microwave in short bursts, stirring until smooth.
Separate the eggs: Crack the eggs and separate yolks from whites into two bowls. Keep whites clean of any yolk.
Mix yolks with chocolate: Add egg yolks to the melted chocolate and stir until fully combined and glossy.
Whip the egg whites: Using a mixer, beat the egg whites until stiff peaks form.
Fold everything together: Gently fold the whipped egg whites into the chocolate mixture in batches, being careful not to deflate the batter.
Bake the cake: Pour batter into a lined or greased baking pan, smooth the top, and bake at 170°C (340°F) for about 25–30 minutes. The center should still feel slightly soft when removed.