75 g (3 oz) Mars Bar or other chocolate bar, cut into 12 slices
Melt the dark chocolate with the butter in a small pan set over a very low heat until just melted.
Meanwhile, whisk the eggs in a bowl with the sugar, then stir in the flour. Pour in the melted chocolate mixture and stir to combine. Divide the mixture between the greased or paper case-lined cups of a 12-cup muffin tin. Push a slice of chocolate bar onto each bun and bake in a preheated oven, 180˚C (350˚F), Gas Mark 4, for about 18 minutes or until almost firm to the touch. Cool in the tin until firm enough to handle. Serve warm or cold.