For the souffle:
1. Preheat the oven to 180°C. Melt half the butter and use to brush the inside of eight small ramekins.
2. Tip 25g of the caster 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.
3. Melt the chocolate with the spices, rum, vanilla extract and remaining butter in a large heatproof bowl over a pan of gently simmering water. Stir until smooth.
4. Remove the bowl from the heat and mix the egg yolks in one at a time. In a large clean bowl, whisk in the egg whites to soft, moist looking peaks, then add the remaining sugar. Mix a little into the chocolate mixture, then gently fold in the rest using a large metal spoon.
5. Divide the souffle mixture between the ramekins, spooning it in, and placing the ramekins on a baking sheet. Bake in the preheated oven for exactly 11 minutes.
For the custard:
1. Put the milk in a pan and heat but do not boil. Put the egg yolks, cornflour and sugar in a bowl and beat together well.
2. Pour the warm milk over the egg mixture and whisk, using an electric hand whisk, until well combined. Return to the pan and stir with a wooden spoon over a low heat until the mixture thickens.
3. Do not let it boil. Pour the custard into a bowl and stir in the Advocaat and vanilla. Put a piece of baking paper on the surface to prevent a skin forming and leave to cool.