Bring the cream and sugar to boil over medium-high heat, then cook for 3 minutes, stirring it with a whisk, turning the heat down or lifting the pot from the burner as it tries to boil over.

Remove from heat and stir in the lemon and lime juice and let it sit for 5 minutes or so to cool a bit. Stir again and divide among six 1/2-cup ramekins or small dishes. Cover (or not) and chill for an hour or two, until set.