Recipe Plum Butter

Cook plums in a large stockpot with enough water to cover the bottom over very low heat for 2 hours, then let cool for 2 hours. Return to low heat for 2 to 3 hours, then let sit at room temperature for 8 hours to overnight. Cook again over low heat for 2 hours and let stand for 2 hours. Bring the mixture to a boil, stir in sugar, and simmer for 15 minutes until thickened. Fill sterilized jars with the plum butter, leaving a 1/4-inch headspace, and remove air bubbles before sealing with lids and rings. Process the jars in a boiling water bath for 15 minutes, ensuring they are covered by at least 1 inch of water. Cool the jars on a protected surface and check the seals before storing in a cool, dark place.