Weigh the fruit. Plums run from about 40 g to 100 g each, so two plums and an apricot is roughly 200 to 250 g. Counting them means two cooks can be more than double apart.
Makes about 300 ml. Enough for four as a sauce. It doubles and triples happily if you have a glut, but allow a few extra minutes to reduce.
Taste it at the end, and reach for the vinegar. If it tastes like ketchup, the balance of sugar to vinegar is the cause, not the fruit. Add vinegar a teaspoon at a time.
It thickens as it cools, so stop while it still looks slightly loose.
Fridge 3 to 4 days, freezer up to 3 months. This sauce contains stock, so it is not a preserve and must not be water-bath canned at any vinegar level. Freeze it instead.