How to boil away water from a sauce without it splashing? When "slow cooking" a certain recipe, I need to keep a lid on the pot, or the sauce slowly but surely splashes all over the place.

However, with the lid on, the sauce retains much more water than I like.

How can I boil away the excess water, or otherwise make the sauce less watery, without incurring significant extra cleaning?
If, when reducing a sauce, you are getting splashing outside the pot, your pot may be too small for the application.  Use a larger pot:  a wider base will allow more surface area for evaporation, and higher sides will make it harder for the content to get out.

You can also purchase a splatter guard, which is like a flat sieve or mesh that you can place over the top of the pot to reduce splatter without blocking air flow



although these are more typically used to reduce the splatter from frying.