STEP 1: PREPARE THE FLANK STEAK

Start by preparing your flank steak. If your butcher hasn’t already done so, remove any silverskin (the tough membrane on the surface of the meat) from the steak. Lay the steak flat on a cutting board, and using a sharp knife, butterfly the steak by slicing it horizontally along the grain, but not all the way through. Open the steak up like a book to create a larger surface area for stuffing.

Once the steak is butterflied, season both sides generously with salt and pepper. Next, rub a thin layer of Dijon mustard over the entire surface of the steak. The mustard not only adds flavor but also helps to keep the beef tender while roasting. Sprinkle fresh rosemary and thyme over the surface of the steak to further infuse flavor.

STEP 2: MAKE THE MUSHROOM FILLING

While the steak is being prepared, make the mushroom filling. Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the chopped onions and sauté for 3-4 minutes until they become translucent and soft.

Next, add the minced garlic and cook for another 1-2 minutes until fragrant. Add the chopped mushrooms to the skillet and cook for about 6-8 minutes, stirring occasionally, until they release their moisture and become golden brown. If needed, increase the heat slightly to get a nice caramelization on the mushrooms.

Once the mushrooms are cooked down, season with a pinch of salt, pepper, and fresh thyme. If you want to add a little more richness, sprinkle in the Parmesan cheese and stir until melted and incorporated. Remove the skillet from the heat and let the filling cool for a few minutes. Then, stir in the fresh parsley and breadcrumbs (if using) to help bind the filling together.

STEP 3: STUFF AND ROLL THE FLANK STEAK

Now that your steak and mushroom filling are ready, it’s time to stuff the steak. Spoon the mushroom mixture evenly over the entire surface of the butterflied steak, leaving a small border around the edges so that the filling doesn’t spill out.

Once the steak is filled, carefully roll it up from one end to the other, ensuring the filling stays inside. You can use kitchen twine to tie the roll together at 1-2 inch intervals to hold it in place during cooking. If you don’t have twine, toothpicks can also work to secure the ends. Be sure to tuck in the sides of the steak as you roll to keep the filling from falling out.

STEP 4: SEAR THE FLANK STEAK

Heat 2 tablespoons of olive oil in a large oven-safe skillet over medium-high heat. Once the oil is hot, carefully place the stuffed and rolled flank steak into the pan. Sear the steak on all sides for 3-4 minutes until it develops a beautiful brown crust. This step helps to lock in the juices and enhance the flavor of the beef.

STEP 5: ROAST THE STEAK

Once the steak is seared, transfer the skillet to the preheated 400°F (200°C) oven. Roast the steak for 20-25 minutes for a medium-rare finish, or until the internal temperature reaches 125°F (52°C). For medium, roast for an additional 5 minutes until the internal temperature reaches 135°F (57°C). Keep in mind that flank steak is best served medium-rare to medium for tenderness, so use a meat thermometer to ensure perfect doneness.

STEP 6: MAKE THE PAN SAUCE (OPTIONAL)

While the steak is roasting, you can make a simple pan sauce to drizzle over the finished dish. After removing the steak from the skillet, pour out any excess fat, leaving just a little bit in the pan. Add the red wine and let it reduce by half over medium heat, scraping up any brown bits left from the steak. Once the wine has reduced, add the beef broth and bring it to a simmer. Let the sauce reduce again for about 5-7 minutes, or until it thickens slightly.

Finish the sauce by whisking in the unsalted butter and fresh rosemary, and season with salt and pepper to taste. Keep the sauce warm while you slice the steak.

STEP 7: REST AND SERVE

Once the steak has finished roasting, remove it from the oven and let it rest for 10 minutes. This allows the juices to redistribute throughout the meat, ensuring it stays moist and tender when you slice it.

After the steak has rested, slice it into 1-inch thick slices. Arrange the slices on a platter and serve with the pan sauce drizzled over the top. Garnish with additional fresh parsley for a pop of color.