Butter an oven-proof dish which will fit the hot cross buns snugly. For this recipe, I have used a dish with a capacity of 1 litre/4 cups.
Slice each hot cross bun horizontally into 3 slices.
Spread some butter and marmalade or jam onto each slice, but leave the top of the buns untouched.
Place the bottom layer of buns into the baking dish.
Pour over one-third of the custard.
Allow to sit for 5 minutes.
Add the middle layer of buns.
Pour over another one-third of the custard.
Allow to sit for 5 minutes.
Add the top of the buns.
Pour the remaining custard all over the buns. Depending on the size of your baking dish, you may not need all of the custard. Leave at least 2 cm from the rim of the dish as the custard will rise a bit during baking.
Sprinkle the buns generously with demerera sugar.