Caramelised onion and bacon quiche

This is the original recipe that I think explains things in a weird order so I’ve written it out bellow in a way that makes more sense to me (and in double quantities)

butter (for the frying pan)

4 onions (chopped as small as you can without worrying about it too much)

350g(ish) shop-bought shortcrust pastry

about 400g veggie bacon (chopped into little bits)

600g pot double cream

200ml milk

6 large eggs

2-3 pinches of nutmeg, plus extra for the top

280g mature cheddar, grated and halved