Since the weight of the plums in the recipe is based on pitted plums, start with 3 pounds of plums. To water-bath can the jam for longer storage, scald about 4 half-pint jars and soak canning lids in a pan of hot water to soften the rubber seal. Pour the jam into jars, leaving a ½-inch space from the rim. Seal with the lids, screw on the bands, and lower into a pot with the rack and enough water to cover the jars by about 1 inch. Bring the water to a boil and process the jars for 10 minutes (start the timer when the water reaches a boil). Remove the jars from the water and cool.
Vanilla Plum Jam
Makes 4 cups
2.1 lb / 945 g pitted, coarsely sliced plums
- 2 cups / 400 g turbinado or granulated sugar
- 1 vanilla bean, split lengthwise
- Juice of 1 lemon
In a large, heavy-bottomed pot or Dutch oven over high heat, bring the plums, sugar, vanilla, and lemon a boil, giving the pot a couple of good stirs. Let sit 30 minutes or refrigerate for up to 5 days. Chill a plate in the refrigerator to test the jam’s thickness later.
Mash the plums with a potato masher to break up the pieces. (The plums will completely lose their shape.) Bring the pot to a boil and continue cook over medium-high heat until the water has reduced to more of a syrup and the color has deepened significantly, 10-15 minutes depending on the pot and the burner strength.
Put a drop or two of the jam on the chilled plate to check if it sets. If the juices run all over, then continue to cook down the jam-but avoid cooking it to a point where the sugars start to caramelize and the jam turns brown. It's OK if the jam is more like a compote for putting on yogurt, etc.
Pour the jam into 2 clean, glass pint jars, one large quart jar, or several small jars and let cool. The jam keeps in the refrigerator for several weeks.