Divide between 6 ramekin dishes. Place in freezer for at least 45 minutes.
Remove from freezer. Preheat grill or broiler to very high. Sprinkle 1 tablespoon of sugar over top of each.
When grill/broiler is ready, cook under grill/broiler until sugar bubbles and turns very dark -- anywhere from 3 to 5 minutes.
Remove, cool a few minutes, then place in refrigerator until ready to serve (if you need it right away, stick back in freezer for about 20 minutes.)
Notes
You can buy ready-made custard either fresh in the chillers of some supermarkets (certainly any in the UK!), or on shelves in Tetra Paks or in tins.If all else fails, haul out that tin of Bird's -- or make your own, if you have the time that day. Or, use vanilla pudding.If you have a kitchen blow torch, you can use that instead of putting it under the grill.