With meat mallet or rolling pin, flatten meat to approximately a 10x8 inch rectangle. Spread mustard over meat. In large skillet, over medium high heat, cook bacon and onion until bacon is crisp; pour off fat, reserving quarter cup.
Spread bacon mixture over meat; sprinkle with pickle. Roll up meat from short end; secure with string. In large skillet over medium high heat, brown beef roll in reserved fat. Place in a 13x9 inch baking dish.
Stir flour into fat in skillet until smooth; gradually stir in beef broth. Cook and stir over medium heat until thickened. Pour sauce over beef roll. Cover, bake in 325 degree oven for 1.5 hours or until done.
Let stand 10 minutes before slicing. Skim fat from sauce; strain and serve with meat.