How to thicken slow cooker recipe sauce
If you're adapting a recipe for a slow cooker, you would normally reduce the liquid. But there's also quite a lot of variation between slow cookers, in terms of how much steam gets out, so even a slow cooker recipe may need adjustment to the liquid. On top of that your tastes may differ from the recipe creators'.

If you want to thicken the sauce while keeping the quantity constant, a little cornflour (US: corn starch) at almost the end can help - mix it up with cold water then mix into the sauce before putting the lid on for a few more minutes. It should be cooked by the time you do this - opening a slow cooker lets out a lot of heat which can extend the cooking time. You can thicken a slow cooked sauce with cornflour at the start, but you tend to get a skin on top. This will disappear in a few minutes if you stir it in.