This is a tasty recipe taken from Sue Lawrence.
350g/12oz dark chocolate (55-60% cocoa solids)
250g/9oz unsalted butter
3 large eggs
250g/9oz dark muscovado sugar
100g/3.5oz plain flour sifted
1 teaspoon baking powder
a pinch of salt
175g/6oz fresh raspberries
Preheat the oven to 170C/325F/Gas 3. Butter a 23cm/9inch square cake tin.
Melt the chocolate and butter together, then cool slightly.
Whisk the eggs until thick, then gradually add the sugar and beat until glossy. Beat in the melted chocolate mixture, then gently fold in the flour, baking powder and salt.
Pour just over half of the mixture into the prepared cake tin. Scatter over the raspberries, then cover with the remaining mixture.
Bake in the preheated oven for about 40 minutes, or until the surface is set. It will be cooked when a coctail stick inserted into the middle comes out with just a little mixture sticking to it.
Remove the cake tin to a wire rack, and allow it to rest for about 20 minutes. Cut the cake into squares and remove from the tin when cold. ( It can be really difficult to wait that long, but they are really fragile to decant whilst still warm.)