How to Make It
Preheat the oven to 325°F.
Warm ¼ cup olive oil over medium-high heat in a large pot. Add the prosciutto, onion, garlic, bay leaves, rosemary, red pepper flakes, and pimentón and cook until tender, about 3 to 5 minutes. If the meat and vegetables start to brown, decrease the heat and cook slowly until tender. Add the nasturtium leaves and cook until wilted. Add the olives, stir, and season with salt and pepper. Transfer the mixture to a flat plate and cool completely. Set the pot aside without washing.
Open the butterflied flank steaks (like a book) and lightly season inside and out with salt and pepper. Divide the cooked filling between the insides of the flank steaks, then place the provolone on top of the cooked filling. Roll the flank steaks into a tight cylinder, making sure to eliminate any gaps. They should be rolled evenly and tightly. Tie with butcher twine at 2-inch intervals.
Add the remaining 2 tablespoons olive oil to the pot, or enough to lightly cover the bottom, and sear the flanks steaks over medium-high heat until nicely golden, 3 to 4 minutes per side. Reserve the steaks on a plate.
Add tomato paste to same pot, decrease the heat to medium, and cook until paste turns a darker shade of red, 2 to 3 minutes. Add the wine and scrape up any darkened bits of tomato from the bottom of the pan. Gently simmer until the wine has reduced to ¼ cup and no longer smells of alcohol, 3 to 4 minutes. Add the chicken stock and cook until slightly reduced, 3 to 4 minutes. Stir to combine and season with salt and pepper.
Return the flank steaks to the pot, decrease the heat, cover, and braise until meat is tender when pierced with a wooden skewer, 2 to 3 hours.
Let the flank steaks cool to room temperature for at least 1 hour, or chill overnight, so they do not lose their shape. Untie the rolls and cut into 1- to 2-inch slices.
Serve with two fried eggs, or soft polenta, a drizzle of good olive oil, and a few spoonfuls of braising broth.