Slow Cooker Chicken Marsala I haven't tried this specific recipe, but have done this for years. Gotta say: NEVER use cornstarch in a long-term cooking project, since once it "breaks" from overheating it'll never thicken again. I recommend flour (simmer-cooked in 7 minutes or over time in crockpots)- plus it doesn't "break" (thin) when you reheat it. I've also had bad luck with the Marsala flavor disappearing over the hours, so I add most at the last 30 minutes to preserve it. This is an even BETTER sauce if you stir in some sour cream at the end too.....