Toast sesame seeds in a dry frying pan over low heat until golden and fragrant. Place seeds in a bowl with the green onions, ketchup, soy sauce, ginger, molasses, salt, curry powder, pepper, 1 cup water and wine vinegar; stir to mix thoroughly. Place meat in a large bowl and pour the marinade over it. Marinate, covered, 2 to 3 hours or overnight in the refrigerator.
To prepare in a slow cooker: Place meat and marinade in the slow cooker, cover, and cook on low for 8 to 9 hours or on high for about 3 hours.
To prepare in the oven or on the stovetop: Remove meat from marinade, reserving, and pat meat dry. Brown meat in a Dutch oven or frying pan. To continue in the oven, place meat and marinade in a covered casserole dish and roast at 300 to 325 degrees for 3 hours. (The roast should be falling apart when it's done.) For the stovetop, place the meat and marinade in the pot and heat until the marinade is boiling. Reduce to a simmer and cover. Cook, turning meat once or twice, for 3 hours. Serve meat with pan juices or make gravy.
To make gravy: Pour pan juices into a 2-cup measure. Skim off fat, returning 2 tablespoons of the fat to the pan. If defatted pan juices do not equal 2 cups, add enough water or chicken broth to reach the 2-cup measure.
Whisk 3 tablespoons flour into the fat in the pan and cook over medium heat on the stovetop until bubbly. Slowly stir in pan juices and cook until gravy thickens, stirring constantly. Put gravy through fine strainer to assure it is lump-free.