Rolled Flank Steak

Combine the unsalted butter and olive oil in a large skillet over medium-low heat. Once the butter has melted, stir in the onions and ½ teaspoon of salt. Cover and cook for 5 minutes. Remove lid and continue cooking, stirring often to prevent burning, until the onions are golden brown, about 30 minutes. Add the mushrooms and continue cooking until onions are deep golden brown and mushrooms are tender, about 10 more minutes. Transfer onions and mushrooms to a large bowl. Place in the refrigerator until completely cooled, about 15 to 20 minutes. 

Set the flank steak on a large cutting board and cover with plastic wrap. Use a meat mallet to pound steak to about ⅛-inch thickness. Season each side with ½ teaspoon of the salt and set aside to rest for at least 10 minutes.

Preheat the oven to 350°F with a rack in the center position.

Remove the plastic wrap from the steak. Position the steak so that the grain runs parallel to the edge of the cutting board, slide butchers twine under the steak, placing a piece about every 3 inches—you'll likely need about 6 pieces.  

Spread the onion and mushroom mixture evenly over the steak, leaving 2 inches around the edge. Layer the provolone on top of the mixture. Starting from the bottom tightly roll the steak towards the top and continue rolling until the steak is seam-side down.

Starting in the middle of the steak, tie the butchers twine to secure the steak. Working outward, continue to tie each piece or twine you placed under the steak. Cut the prepared steak roll in half and season the outside of the steak roll with the remaining teaspoon of salt.

Heat a large cast iron skillet over medium high heat. Once smoking, set the steak rolls in the skillet, seam-side up first, and brown for 3 minutes on each side, 9 minutes total. 

Transfer the skillet to the preheated oven and cook until the internal temperature reaches 130°F, about 10 minutes. Remove from the oven, transfer steak to a large platter and allow to rest for 10 minutes. 

While the meat is resting, make the pan sauce. Over medium heat, add the garlic and cook, stirring often, until fragrant, about 1 minute.  Add the white wine and increase the heat to medium-high. Bring to a simmer, scraping up any brown bits from the pan. Add the thyme and cook until the liquid has reduced to about a ¼ cup, about 4 to 5 minutes. Stir in the heavy cream and bring the sauce back up to a simmer. Cook, stirring often, until the sauce thickens slightly, about 2 minutes. Whisk in the salted butter and season with freshly cracked black pepper to taste. Transfer to a small bowl.

Remove the twine and cut steak into 1-inch slices. Transfer to a platter, season with freshly cracked pepper and top with fresh parsley. Serve with the garlic-wine sauce alongside.