Slice steak horizontally into 4 quarter-inch thick filets. Spread brown mustard on one side of each steak. Place 2 strips of bacon on each steak. Quarter 1 pickle lengthwise to create 4 pickle spears; set aside. Slice remaining 3 pickles into very thin wheels. Spread thin pickle slices over steaks, covering all.
Peel, halve, and slice onion. Melt 1 Tbsp. butter in medium hot skillet. Saute onion in skillet until golden brown. With tongs, spread sauted onion evenly over the four steaks. Set skillet aside.
Starting at narrowest end of steak, roll each around a single pickle spear. Tie each roll closed with two pieces of cooking string.
Melt 2 Tbsp. butter in onion skillet on medium high heat. Place beef rolls in skillet. Turn beef rolls in skillet; brown well on all sides. Add beef broth to skillet. Cover skillet and reduce heat. Simmer, covered, for 60-80 minutes.
Remove Rouladen from skillet; Cut and remove string. Increase heat to high. Reduce broth in skillet by half to create sauce. Drizzle sauce over Rouladen and serve.