Trim off outside leaves of cabbage. Cut off a slice about and inch. Cut core from cabbage with a sharp knife, then hollow out cabbage.
Chop cut out pieces coarsely and cook as a vegetable for another day. Spoon meat mixture into shell; fit cut slice back into place; tie with string.
Place stuffed cabbage, core end down, in slow cooker; add boiling water. Cook on low for 8 hours or on high for 4 hours or until cabbage in tender.
Turn heat control to high. Combine 3 tablespoons flour and 1/3 cup cold water in a cup. Pour in pot. Season to taste with salt and pepper. Darken with a few drops of bottle gravy.
Place stuffed cabbage on a heated serving platter; remove string.
Cut cabbage into wedges; spoon gravy over