Pat meat dry and season well with pepper and coarse salt on both sides. Separate meat into 2 or 3 even pieces at the natural seam where this a layer of fat. Trim most of the fat, leaving just a thin layer. Tie each piece with butchers twine so it stays together during cooking.
In a separate pan or in the slow cooker if it has a sauté function, sear the meat in the oil on med/high heat until each side has a nice crust. Transfer meat to a plate.
Add onion, celery, 1/2 tsp salt, 1/4 tsp pepper to the pan and sauté until softened and lightly browned, about 8 minutes.
Stir in garlic, tomato paste, thyme, onion powder, umami blend, and cook for 1 minute.
Slowly stir in wine and broth, scraping up any brown bits at the bottom of the pan. If you used a separate pan, transfer to slow cooker now.
Add in potatoes and carrots, nestle the meat into the veggies and pour the accumulated juices from the plate over the meat. Add bay leaves. Cover with lid and set to low for 9-10 hours or high for 6-7 hours.
Transfer meat to a carving board and cover with foil. Let rest for 20 minutes before cutting.
Transfer veggies to a platter. Tent with foil.
Add minced parsley to the slow cooker sauce.
Remove butchers twine and slice meat into slices against the grain. Transfer to platter and top with 1-2 cups of the sauce from the slow cooker.