Cranberry Marmalade - orange mediums

Method

• First, prepare fruit. Cut 2 medium oranges and 1 medium lemon in quarters. Remove seeds. Grind the fruit, chop fine or slice crosswise wafer thin. Add 1 1/2 cups water and 1/8 teaspoon baking soda. Simmer, covered, 20 minutes, stirring occasionally. Add 1 pound fully ripe cranberries; simmer, covered, 10 minutes. Measure 5 cups into a very large saucepan.
• To the measured fruit in saucepan, add the exact amount of sugar specified in the recipe. Mix well.
• Place over high heat, bring to a full rolling boil and boil hard 1 minute, stirring constantly. Remove from heat; at once stir in Certo. Skim off foam with metal spoon. Then stir and skim for 7 minutes to cool slightly and prevent floating fruit.