Melt half the butter and use to brush the inside of eight small ramekins.
Tip 25g of the sugar into one ramekin and tap around the sides to lightly coat. Pour the excess into the next ramekin and repeat until all the ramekins are butter-and-sugar-coated.
Melt the chocolate with the spices, rum, vanilla extract and remaining butter in a large heatproof bowl, over a pan of gently simmering water (the base of the bowl must not touch the water). Stir until smooth.
Remove the bowl from the heat and mix the egg yolks in one at a time.
In a large clean bowl, whisk the egg whites to soft, moist-looking peaks. Mix a little into the chocolate mixture, then gently fold in the rest, using a large metal spoon.
Divide the soufflé mixture between the ramekins, spooning it in, and place the ramekins on a baking sheet. Bake in the preheated oven for exactly 11 minutes.
Serve with hot vanilla custard poured into the centre of each soufflé.
These soufflés must be cooked just before eating; they will flatten within 2 minutes of being removed from the oven. Be careful not to open the oven during cooking, as this may prevent them from rising.
Recipe courtesy of Home Bake published by Mitchell Beazley.