Melt chocolate and butter in a heatproof bowl set over a saucepan of simmering water, or in the microwave. Stir until smooth. In a bowl, beat the eggs, sugar and vanilla. Stir in the chocolate mixture. Combine flour, bicarbonate of soda and salt. Gradually add to the chocolate mixture, then fold in the raspberries. Spoon into the tin, level the top and bake for 25–30 minutes, or until a skewer inserted in the centre comes out clean (do not overcook). Cool in the tin on a wire rack.