Preheat your oven to 375°F (190°C) and grease a 9-inch springform pan. Line the bottom with parchment paper.

1. Melt the dark chocolate and butter together in a heatproof bowl over a pot of simmering water (double boiler method). Stir until smooth and remove from heat.
2. Stir in the granulated sugar and let the mixture cool slightly.
3. Add the eggs one at a time, beating well after each addition.
4. Sift in the cocoa powder and salt, then gently fold the mixture until fully combined.
5. Gently fold in half of the wineberries, saving the rest for garnish.
6. Pour the batter into the prepared pan and smooth the top.
7. Bake for 25–30 minutes, or until the top is set and the center is slightly jiggly.
8. Let the cake cool in the pan for 10 minutes, then remove the springform ring and allow it to cool completely.
9. Garnish with the remaining wineberries and dust with powdered sugar if desired.