Step 1Preheat oven to 170 °C/ 340 °F (conventional), or 150 °C/ 300 °F (fan assisted). Line the base and sides of a 20 cm/ 8" springform pan with non-stick baking paper.
Step 2To make the cake, roughly chop the chocolate and the butter, and add in a saucepan over low heat. Stir until melted. Add the vanilla and stir through.