In a small pot over medium-low heat add berries, basil leaves, lemon juice and zest and honey. Cook for 5–10 minutes, or until juices begin to release from berries. Then add crème de cassis and, if using, ginger.Continue to cook down until berries are softened and all has blended together. Keep an eye on it, though, because if left too long it can caramelize.Should store in the fridge for up to a week, and can also be canned.