• Separate 4 eggs, putting the yolks into a large bowl.
• Add the caster sugar (30g) and whisk until combined.
• Add the plain flour (30g) and vanilla extract (¼tsp) and whisk until combined.
• Heat the milk (300ml) on a very gentle heat until warmed but not quite boiling. Stir regularly to ensure that it doesn't burn.
• Once the milk is warm, remove it from the heat and gradually add it to the egg yolk mixture a bit at a time. Whisking in each addition before adding more.
• Once combined, put the mixture into the pan and return it to a gentle heat. Break up the chocolate into squares (55g milk chocolate and 25g dark chocolate) and add it to the pan. Cook the custard, whisking constantly until the custard reaches your desired thickness - this usually takes about 10 minutes but depends on exactly how thick you'd like the custard to be.
• Remove the custard from the heat and serve.

If you're making the custard in advance

• Put the custard into a bowl or jug and cover with cling film. It is important that the custard is in full contact with the clingfilm to stop a skin forming as the custard cools.
• Put the custard into the fridge until it's needed.
• To reheat the custard, simply pour into a pan and warm over a gentle heat until it's nice and hot. You may find that it gets a little thicker than you'd like. If it does then simply whisk in a little extra milk to thin it down a bit.