For best results, use ripe strawberries and fresh, firm rhubarb. Chop the fruit into small, even pieces so it cooks down evenly. If you prefer a smoother texture, mash the jam slightly while it's cooking or blend it briefly at the end. This recipe makes about 3 cups of jam, or roughly 24 servings (2 tablespoons each). Store in the refrigerator for up to 3 weeks or freeze for longer storage.