Remove the fell (tissue-like covering) from lamb with a sharp knife. Place lamb, fat side up, in a shallow roasting pan. Rub surface of lamb with lemon juice. Make several small slits on outside of lamb, and stuff with garlic slices.
Combine flour, salt, pepper, and paprika; mix well. Sprinkle flour mixture over lamb, coating well. Insert meat thermometer, if desired.
Bake, uncovered, at 400° for 15 minutes; reduce heat to 325°. Continue baking until desired degree of doneness: about 1 hour and 40 minutes or 140° (rare); about 2 hours or 160° (medium); about 2 1/2 hours or 170° (well done).
Transfer lamb to a warm serving platter. Let stand 10 minutes before slicing. Serve lamb with mint or red currant jelly.