How do I convert a recipe given as a slow-boiled stew to a slow-cooker recipe? I assume that liquid amounts and probably onions and other flavorings need to change. What are those changes? What proportions? Are there particular ingredients I should watch out for?
Stewing or braising is essentially what slow cookers do, so there is not a huge difference in converting a stew recipe.
There are two main issues to consider:
Flavor development. You may choose to sear or brown your ingredients separately, and then deglaze for your base sauce. Most slow cookers cannot create the browning, so it would need to be done separately.
Liquid level. If your original recipe stews with an open lid, you will get less evaporation in the slow cooker, so may want to reduce the liquid slightly to compensate.