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 (½ tsp) and whisk until combined.
Gently heat the milk (300ml) until warm but not boiling and then gradually add it into the egg yolk mixture a bit at a time whisking in each addition completely before adding more.
Once combined, pour the mixture back into the saucepan and return to a very gentle heat. Continue to cook, whisking continuously, until the custard has reached your desired thickness (this usually takes about 10 minutes).
Add the orange oil (¼ tsp) and brandy (2 tbsp) and whisk to combine.
Remove from the heat and pour the custard into a bowl or jug and cover with clingfilm. It's important that the clingfilm is in full contact with the surface of the custard to stop a skin forming.
Refrigerate the custard until you're ready to use it.
Once you're ready to serve, pop the custard into a pan and gently heat until warm (whisking constantly). If you find that the custard gets a little too thick then simply thin it out with a little extra milk.