Dredge the oxtail pieces in flour and sear them in very hot oil to brown. Transfer to the slow cooker.

In the same oil, sauté the vegetables. Add the wine and bring to a boil until it reduces. Add the bay leaf, salt, and pepper, then transfer everything to the slow cooker.

Cook on low for 7 hours. Remove the meat and set aside. Blend the vegetables with the cooking juices, then serve the meat topped with the sauce.