Add cranberries, strawberries, granulated sugar, light brown sugar, ground allspice, cinnamon, and ginger to the crockpot. Stir everything thoroughly to combine the ingredients evenly.

Cover the crockpot and cook the mixture on high heat for four hours. Stir the jam halfway through cooking to ensure even heat distribution and prevent sticking.

Once cooked, use an immersion blender directly in the crockpot, or carefully transfer the hot mixture in batches to a countertop blender. Pulse just two to three times to achieve a thick, jam-like texture without completely pureeing all the fruit.

Ladle the hot jam into clean, sterilized jars. Wipe the rims clean and screw on the lids lightly to allow slight expansion as the jam cools.

Allow the jars to cool at room temperature, then refrigerate the jam overnight before serving to let the flavors meld and the jam set properly.