Preheat the oven to 180 degrees C

Grease and line a 20cm springform pan with softened butter or nonstick cooking spray.

Combine the butter, chocolate and tahini in a large heatproof bowl. Set the bowl over a small pot of simmering water and heat, stirring often, until the chocolate and butter have melted and you can stir everything together to a smooth, creamy mixture

Remove from the heat and set aside

Separate 4 of the eggs, placing the whites in a large, clean and dry mixing bowl

Place the yolks in another large bowl and add the almond flour, cocoa powder, salt, and the remaining 2 whole eggs and whisk to blend well

Using a spatula, gently and gradually mix the egg yolk mixture into the melted chocolate mixture

With the mixer on high, beat the egg whites until light and foamy

Gradually add the sugar (excl the 2 tablespoons), a tablespoon or two at a time, and continue to beat until egg whites have tripled in volume and hold stiff peaks

Using a spatula, gently fold the egg whites into the chocolate mixture until just combined and no white streaks remain, making sure not to overmix

Pour the batter into the prepared pan and smooth the top

Sprinkle with the remaining 2 tablespoons granulated sugar and bake until the edges begin to pull away from the sides of the pan and the top looks puffed and lightly cracked, like a soufflé (it should still have a little jiggle), about 35 to 40 minutes.

Place on a wire rack and let the cake cool down

The center of the cake will collapse, causing further cracking around the edges

Whip the sour cream and nutella together and spoon on top of the cake

You can bake this cake up to 2 days ahead, wrap it tightly, and store at room temperature. The flavour will improve as it stands. Add the topping only when ready to serve.

Adapted from Alison Roman