Season the steak with salt, pepper, garlic powder, and onion powder.
Heat the olive oil in the bottom of a large heavy-bottomed skillet over medium-high heat. Add the seasoned steak to the pan and sear on one side for 2 minutes. Flip and sear on the other side for 2 minutes.
To the bowl of an instant pot, add the onion, thyme, and rosemary followed by the seared steak. Whisk together the brown gravy mix, beef broth, and Worcestershire sauce. Pour it over the beef. Arrange the slices of butter over the beef.
Seal the instant pot and cook on high pressure for 1 hour and 10 minutes. Allow the pressure to release naturally.
Using tongs, transfer the beef to a cutting board. Shred the beef with two forks and return it to the warm pressure cooker while you prepare the rolls.
Preheat the oven to 350℉. Wrap the French rolls in aluminum foil and heat in the oven for 10 minutes.
Slather 1 tablespoon of mayonnaise on one side of each roll and 1 tablespoon of mustard on the other. Using a slotted spoon, scoop the beef into the rolls (try to divide it evenly between the rolls). Discard the cooking liquid. Top the beef with tomato slices, shredded cabbage, and pickles.
Notes
If you have any leftover meat from this Italian beef sandwiches recipe, then all you need to do is place it in an airtight container and store it in the fridge for up to 4-5 days or in the freezer for up to 3 months.