2 lb. flank steak (ex: bottom round, but see note, above)
Kosher salt and freshly ground black pepper
1 cup grated mozzarella
3/4 cup freshly grated Parmigiano-Reggiano
1/3 cup Panko breadcrumbs
28 large fresh basil leaves, en chiffonade
1/4 cup olive oil
1 large yellow onion, diced
1/2 cup red wine
One 28-oz. can diced tomatoes and their juices (3 cups)
1/4 tsp. crushed red pepper flakes
8 oz. button mushrooms, quartered
- On a large cutting board, slice the steak lengthwise along one side, without cutting all the way through the meat, and open it up like a book. Using a meat mallet, flatten the meat so it is about 1/4 inch thick. Sprinkle both sides of the meat with salt and pepper.
- Combine the mozzarella, Parmigiano, breadcrumbs, and basil for the stuffing, and sprinkle evenly over one side of the beef, and roll it up lengthwise, jelly roll–style, with the stuffing inside. Secure with kitchen twine in a few places.
- Heat half the oil in a large Dutch oven over medium-high heat until it’s shimmering. Add the beef and cook until it browns and releases easily from the pan, about 2 minutes. Flip and cook the other sides until browned as well. Transfer to a large plate.
- Add the remaining oil and the onion to the pan, and lower the heat to medium. Sprinkle with 1/2 tsp. salt and cook, stirring, until the onion wilts completely and turns a light brown, about 8 minutes. Add the red wine and cook, stirring, until it almost completely reduces. Add the tomatoes and red pepper flakes and bring to a boil. Reduce to a gentle simmer and tuck the meat and mushrooms into the broth. Cover and cook, repositioning the meat occasionally, until the meat becomes tender and cuts easily with a paring knife, about 1-1/2 hours. Set the meat on a cutting board and let rest for 10 to 15 minutes. Thinly slice and serve topped with the sauce and vegetables.