You will need: a 22–23cm / 9-inch springform cake tin. Arrange the oven shelves so that one is in the middle for the cake, and another just below it. Slide a baking sheet onto the lower rack to catch any drips as the cake bakes. Heat the oven to 180°C/160°C Fan/350°F.Butter a 22–23cm / 9-inch springform cake tin and line the base with baking parchment. Mix the flour and cocoa powder together in a bowl, and set aside.Put the butter, liqueur if you are using it, sugars, chocolate, coffee and water in a thick-bottomed saucepan and stir over low heat until everything melts and is thickly, glossily smooth. Remove the pan from the heat, and let stand for a couple of minutes.Stir the flour and cocoa mixture into the pan, and beat well — just with a spatula or wooden spoon — until all is smooth and glossy again, then gradually beat in the eggs. The mixture will be runny: don’t panic, and don’t add more flour; the chocolate itself sets as it cooks and then cools.Pour into the prepared tin until you have covered the base with about 2cm of the mixture (which will be about half of it) and then cover with the raspberries and pour the rest of the mixture on top. You may have to push some of the raspberries back under the cake batter by hand.Put into the preheated oven and bake for 40–45 minutes. Don’t try and test by poking in a skewer as you don’t want it to come out clean: the gunge is what the cake is about. But when it’s cooked, the top will be firm, and slightly cracked. Don’t worry about that: a little icing sugar will deflect attention. When it’s ready, take the cake out of the oven and put on a rack. Leave in the tin for 15 minutes before removing the sides of the tin; the cake must stay on its base.When you’re just about to eat — and this should be around an hour after the cake’s come out of the oven — dust with a little icing sugar pushed through a tea strainer. Serve with lots more fresh raspberries, and Greek yoghurt, whipped double cream or crème fraîche as wished.