Start by washing 12 ounces of fresh cranberries and 16 ounces of strawberries. Remove stems from strawberries and slice into halves or quarters for even cooking. In a bowl, combine cranberries, strawberries, 1 cup of granulated sugar, 1/2 cup light brown sugar, 1 teaspoon each of ground allspice, ground cinnamon, and ground ginger. Stir until well-coated.

Pour the fruit mixture into your slow cooker without exceeding the two-thirds full mark. Cover and set to high heat. Cook for approximately 4 hours, stirring halfway through.

After 4 hours, check the mixture. It should be aromatic and bubbling, with softened cranberries. Blend mixture using an immersion blender for 2-3 pulses until thick and spreadable.

Ladle the warm jam into clean, sterilized jars. Wipe rims for a proper seal and secure lids loosely.

Let jars cool at room temperature for about 1 hour. Refrigerate afterwards, allowing the jam to thicken further overnight.