1 bone-in turkey breast
1 medium yellow onion, thinly sliced
generous splash of brandy or chicken stock
1-2 tablespoon(s) butter
salt & pepper
herbs de provence or poultry seasoning (optional)
Spray the insert of your slow cooker with cooking spray.
Heat a generous splash of olive oil in a large skillet (avoid nonstick if possible) over medium to medium high heat. Place the turkey in the skillet and allow to brown (give it several minutes before checking - if it seems to be sticking to the pan, let it alone for a few more minutes). While browning, sprinkle the bird generously with salt and pepper, inside and out. With a large tongs, flip the turkey over and continue browning as many sides as you're able to, holding the bird in place with your tongs if necessary. Season with more salt and pepper while browning.
Carefully transfer the bird to the slow cooker (it's easier if you remove the insert and place it next to the skillet) with the tongs. Sprinkle the bird with herbs de provence or poultry seasoning, if desired.
Add a little more oil to the skillet if needed. Add sliced onions and cook to soften and/or brown, if desired. When the onions are soft, add a generous splash of brandy to the pan (off heat, especially if using a gas stove). Using a wooden spoon or silicone cooking utensil, scrape up any remaining brown bits on the bottom of the pan. Add the butter and allow to melt; transfer contents to slow cooker.
Cover the turkey and cook on low for 8-10 hours, or high for 4-5 hours. Carefully remove the bird from the slow cooker to a cutting board designed for meat (it will have a ridge around the outside to catch juices). Allow to cool a bit before pulling the meat apart with your hands. (Keep on the lookout for bones during this process - there are some small ones that may have broken off.)
If desired, serve with mashed potatoes and gravy.