Tart Cherries: You can swap tart cherries in for dark sweet cherries in the same quantity if desired. You'll need to add a bit more sugar to taste. I would start with the 1/3 cup, and then stir more in at the end of cooking, 1 tbsp at a time, to taste. Don't worry - it will dissolve into the sauce just fine, even if you stir it in at the end. I do it all the time.