[Day 1] (Make the batter a day in advance) Mix 160ml milk, 50g butter, 10ml vanilla, 20g sugar in a saucepan and bring to a simmer over a medium heat. Remove from the heat and let cool to about 38C
Whisk in the egg mixture
Whisk in the rum and 310ml milk.
Mix the flour, 210g sugar and 1/2 tsp salt together in a bowl.
Whisk dry into wet in thirds. Avoid over-whisking. Should have the same
consistency as double cream.
Cover with clingfilm directly on the surface in the fridge overnight.