Mix all ingredients in a heavy medium pot. Cook over low heat, stirring occasionally, until fruit releases juices, about 30 minutes. Continue to cook, stirring as needed to prevent sticking, until thick and slightly darker, about 1 1/2 hours.
Chill jam in airtight containers up to 1 month, freeze up to 6 months, or process according to Sunset canning methods (sunset.com/canning).
MAKE IT YOUR OWN
Try these variations:
Rose: Stir in 2 to 2 1/2 tsp. rose water at the end.
Rhubarb: Replace 1 lb. strawberries with chopped rhubarb.
Black pepper: Simmer berries with 2 tsp. crushed peppercorns.