Slow Cooker

A slow cooker is not a machine that cooks food slowly. It is a machine that converts collagen into gelatin, and once you know that, the whole appliance makes sense.
Collagen is the connective tissue in muscles that work hard. Shoulders, shanks, chests, the parts of the animal that never get to rest. Hold that tissue at low temperature for long enough and it breaks down into gelatin, which is what gives a properly cooked chuck roast its richness. The meat did not simply get soft. Something inside it turned into something else.
This is why the same appliance produces fall-apart pot roast and completely inedible chicken breast. A lean, fine-grained cut has almost no collagen, so there is nothing for the machine to convert. It spends eight hours removing water instead. That is not a bad recipe. That is the wrong cut, and no amount of seasoning will rescue it.
What belongs in the pot
Chuck roast is the best thing you can put in a slow cooker, and it is also one of the cheapest cuts in the case. Pork shoulder, often labelled pork butt, is the most forgiving. Brisket, short ribs, beef shank and corned beef all work for the same reason. Bone-in chicken thighs are the only chicken worth slow cooking, because dark meat carries enough fat and connective tissue to survive five hours.
Pork loin sits on the edge. It works if you pull it at 145°F internal, which usually lands around four hours on low rather than the eight a recipe written for chuck will tell you.
Pork tenderloin and chicken breast do not belong here at all. Those go in the air fryer.
Four things that apply to every recipe below
Sear first. Browning does not happen below roughly 285°F, and a slow cooker never gets there. Six minutes in a hot pan is the difference between pot roast and boiled beef.
Use less liquid than you think. Slow cookers barely evaporate. A recipe converted from the oven usually needs its liquid cut by about half.
Leave the lid alone. Every time you lift it you lose roughly twenty minutes of cooking.
Add dairy at the end. Milk, cream and sour cream split over long cooks. Last thirty minutes.
Every recipe here is sorted by cut, with the cook time that actually applies to that cut, taken with a probe thermometer rather than estimated.