I tried out an oxtail recipe recently and it turned out great in the slow cooker; this is off the top of my head so I don't remember the exact measurements of all the ingredients. It makes a nice hearty stew which you can thicken up with a roux and serve over pasta (thicker noodles like pappardelle work great). The oxtail also has a lot of collagen in it, which adds richness and is supposedly packed with health benefits.
Ingredients for a 6-quart crockpot:
1.5 lbs oxtail on the bone
3 large carrots
One bunch of celery
One large leek
One large white onion (can be substituted for pearl onions if you want whole small onions in the stew)
Chicken broth (one carton should do, you want enough to cover your mixture)
4.5 oz tomato paste
Dry white wine
One large orange
Pasta (egg pappardelle preferred)
Here's the general procedure, remember to season each part individually as that will help maximize the flavor.
Chop up all your vegetables. You want large chunks of everything, as they're going to be cooking for quite a while and will break down. Set aside half of the garlic and parsley for the eventual garnish. Sear your oxtail on a stovetop in oil or butter, then remove it from the stovetop and place it directly in your slow cooker. Don't clean your pan out; you're going to use those drippings to sear half of your garlic and the chopped vegetables (onions, carrots, celery, leeks). Dump all of these over the oxtail, then fill up the slow cooker with chicken broth. Add a generous amount of white wine (I used about half a bottle for a six quart crockpot) and drink the rest of the bottle. Enjoy. Add grated ginger, your entire tube of tomato paste, the juice of your orange (save the skin), and salt+pepper to taste. Add some paprika for heat, and a mixture of basil, sage, oregano (fresh if you've got it, Italian seasoning if you don't). Tie your bay leaves/thyme into a bouquet garni for easy removal and add it to the slow cooker. Give it a bit of a stir, then set it to low for 6-8 hours.
Garnish with a mixture of fresh chopped parsley, garlic, and zest from your orange. If you are serving this over pasta, you can thicken it up with a roux (depending on how much broth you added), and grate fresh parmesan over the top.