Oh the beautiful blackberry! This sauce has spectacular blackberry flavor with just the perfect sweetness from the berries and sugar along with a touch of tartness from the lemon. I use unsweetened frozen blackberries for this recipe as their flavor is consistently good; the berries are picked at their peak and then quickly frozen to ensure high quality fruit. Use this blackberry dessert sauce with vanilla ice cream or yogurt, or use as a cheesecake topping.