1 hr. 15 min.
Juice 1 tbsp. fresh lemon juice.
Add lemon juice and 1 cup mixed blue and blackberries to an enamel or stainless steel sauce pan and cook them over a medium flame.
Just as you begin cooking, mash the berries with a potato masher, making sure to leave some berries chunkily mashed. Allow to cook for about 3 minutes until bubbling.
Add 1¼ cup sugar, stir and increase to a high flame. Bring to a bubbling boil. Once the berries are boiling, reduce to a medium simmer for about 5 minutes. Continue to stir.
If the jam still appears to be very liquidy after that 5 minutes of simmering, add 2 tsp. cornstarch. Give it a nice stir and let it cook for another 2 minutes on a simmer.
If you’ve cooked it properly and it’s still runny, simply strain a bit of the liquid. Add to a jar and refrigerate.