1. Preheat oven to 400°F (200°C). Grease a 9-10 inch (22-24 cm) springform pan and line the bottom with parchment paper.

2. Melt the butter in a saucepan over low heat. Remove from heat and stir in the chocolate until smooth. Let cool slightly.

3. In a separate bowl beat the eggs and muscovado sugar with a hand mixer on high speed for 5 minutes until pale and thick.

4. Beat in the salt and vanilla extract.

5. Gently fold the chocolate mixture into the egg mixture until just combined.

6. Pour half of the batter into the prepared pan. Scatter the frozen raspberries evenly over the batter.

7. Pour the remaining batter over the raspberries.

8. Bake for 25-30 minutes until the top is set and a toothpick inserted near the edge comes out with moist crumbs.

9. Let the cake cool in the pan on a wire rack for 1 hour then remove the sides of the pan.

10. Cool completely before serving.

11. Serve with lightly whipped cream and extra fresh raspberries