Cut steak in half crosswise. Season with the salt and pepper.
Heat the olive oil in a nonstick or stainless steel pan over medium heat for 1 minute. Add 1 portion of steak and cook until a golden brown crust has formed, 4-5 minutes per side. Transfer the seared steak to a plate and repeat with the remaining portion of steak. If the pan is getting too dry, add a bit more olive oil. Let the steaks rest for 3 minutes.
After the steak has rested, transfer to a cutting board and pour any accumulated meat juices from the plate back into the pan and return to medium heat.
Add the beef broth and scrape up any brown bits from the bottom of the pan. Add the mustard and butter and stir until combined. Stir in the capers and cook until the sauce thickens slightly, 1-2 minutes.
Slice the steak into ¼-inch (6 mm) pieces and transfer to serving plates. Pour the sauce over the steak and serve with rice and broccoli.