Achieving the correct viscosity for this butter can be tricky, since the cooking time varies according to the ripeness of the plums. After the butter is simmered, it should have the thickness of heavy cream, and once it cools a bit, it should drip thickly from a spoon.
- 1 orange
- 4 lb. plums
- 3 1/4 cups sugar
- 1/2 tsp. vanilla extract
- 1/2 tsp. ground cinnamon
Have ready 5 hot, sterilized half-pint jars and their lids.
Using a vegetable peeler, cut 4 strips of zest from the orange, each about 1 inch wide and 4 inches long. Cut the orange in half and squeeze enough juice to measure 1/4 cup. Pour into a large nonreactive saucepan.
Halve and pit each plum and cut each half into 3 pieces. Place the pieces in the saucepan, add the sugar and stir gently to combine. Bring to a boil over medium-high heat, stirring to dissolve the sugar. Reduce the heat to medium and simmer, uncovered, stirring often, until the plums are tender, about 5 minutes.
Working in batches if necessary, pass the plums through a food mill or fine-mesh sieve set over another large nonreactive saucepan. Stir in the vanilla and cinnamon and bring to a boil over medium-high heat. Reduce the heat to low and simmer, uncovered, stirring frequently, until the butter is the consistency of heavy cream, 55 to 70 minutes.
Ladle the hot butter into the jars, leaving 1/4 inch of headspace. Remove any air bubbles and adjust the headspace, if necessary. Wipe the rims clean and seal tightly with the lids.
Process the jars in a boiling-water bath for 10 minutes. The sealed jars can be stored in a cool, dark place for up to 1 year. If a seal has failed, store the jar in the refrigerator for up to 2 months. Makes 5 half-pint jars.
Adapted from The Art of Preserving, by Lisa Atwood, Rebecca Courchesne & Rick Field (Weldon Owen, 2010).