Preheat your oven to 350°F (175°C). Line a 9-inch (23 cm) round cake pan with parchment paper, ensuring the bottom is fully covered and the sides are lined.
Melt the chocolate and butter. In a heatproof bowl, combine the chopped dark chocolate and butter. Melt gently over a double boiler or in short 20-second bursts in the microwave, stirring after each interval until smooth. Stir in the cocoa powder and salt and set aside to cool to room temperature.
Beat the eggs and sugar. In a large mixing bowl, combine the eggs and sugar. Using a hand mixer or stand mixer fitted with the whisk attachment, beat on high speed for 7-10 minutes, until the mixture becomes very fluffy, pale, and thick. The volume should increase significantly, and there should be no large bubbles visible.
Incorporate the chocolate mixture. Once the chocolate mixture has cooled, gently fold it into the whipped eggs using a spatula. Fold carefully to preserve as much air as possible. Continue folding until fully combined and no large streaks remain.
Bake the cake. Pour the batter into the prepared 9-inch pan. Bake at 350°F (175°C) for 37-40 minutes, until the cake is set and the toothpick comes out dry, a few crumbles are ok. The cake will rise significantly while baking and will deflate as it cools—this is normal.
Cool completely. Let the cake cool in the pan for about 10 minutes, then carefully transfer it to a wire rack to cool completely.
Serve. Once cooled, dust with powdered sugar and garnish with fresh raspberries and blueberries. Serve as is, or add a dollop of whipped cream if desired.
Notes
Chocolate options: Use high-quality dark chocolate with at least 70% cocoa for the best flavor. For a slightly milder taste, you can use 60% cocoa chocolate.
Butter substitute: If you prefer a dairy-free version, substitute the butter with an equal amount of coconut oil or dairy-free butter.
Sugar alternative: You can use coconut sugar in place of regular sugar.
Texture variation: For a creamier center, bake for 35 minutes instead of 37-40. For a more set texture, bake for the full 40 minutes.
Make it dairy-free with a butter substitute: Substitute butter with an equal amount of coconut oil or dairy-free butter.
Serving suggestions: This cake pairs well with vanilla ice cream, a drizzle of caramel sauce.
Storage: Refrigerate for up to 5 days. Bring it to room temperature before serving for the best texture, but I actually loved it cooled right from the fridge.
Preparation & Baking Tips
Melt chocolate properly: Melt chocolate and butter gently over a double boiler or in short microwave bursts, stirring frequently to prevent burning.
Whip eggs and sugar well: Beating the eggs and sugar until thick and pale creates the structure needed for a light yet rich cake.
Fold gently: Carefully fold the chocolate mixture into the whipped eggs to maintain as much air as possible for a delicate texture.
Don’t overbake: The cake should be set but still slightly soft in the center. A toothpick should come out with a few moist crumbs.
Expect deflation: The cake will rise in the oven and collapse as it cools—this is normal and gives it a fudgy texture.
Cool completely before serving: Let the flourless chocolate cake fully cool before slicing to allow the structure to set and the texture to firm up. When hot, the cake is very delicate and may fall apart or have a too-soft, gooey consistency. Cooling helps it achieve the dense, fudgy texture it's known for.