Cranberry Ice Cream

1 pound fresh or frozen cranberries
1/2 to 3/4 cup granulated sugar
1 1/4 cups whipping cream
2 tablespoons plain yogurt

Put cranberries in a saucepan and pour 1 cup boiling water over. Cover and leave for 5 minutes. Bring to simmering point, cook for 5 minutes, turn off the heat and leave for 5 minutes. Bring to simmering point again and cook for 5 minutes. Remove from the heat, stir in the sugar, and reduce to a pur