Sugar melts and becomes liquid at around 320°F. Keeping it hot for a further 10 minutes or so makes it caramelize so it goes crisp and sets. You can either have this crème brûlée for two a couple of inches from a hot broiler or use a kitchen blow torch, which is a little quicker. If you’re using the broiler method, keep your eye on them. They can turn from perfectly crisp to burned fast! When I make these I preheat the broiler to 500°F before putting them underneath. It typically takes around 8 to 10 minutes until they’re completely done. If you can tap the sugar topping with a teaspoon and it’s hard, not runny, they’re ready to serve.