Braised White Beans And Greens With Parmesan

¼cup olive oil
1small fennel bulb, trimmed, cored and small-diced
1small yellow onion, small-diced
2teaspoons minced fresh rosemary or thyme
5garlic cloves, minced
¼teaspoon red-pepper flakes, plus more to taste
1large or 2 small bunches escarole, kale or Swiss chard, stems removed (10 to 12 ounces)
2(15-ounce) cans cannellini beans, rinsed
2cups low-sodium vegetable or chicken broth
Kosher salt and black pepper
1tablespoon lemon juice
½cup shredded mozzarella (optional)
3tablespoons grated Parmesan or Pecorino Romano, plus more for serving
Toasted country bread, for serving
1/2 pound Italian sausage, removed from its casing

In a 12-inch skillet or Dutch oven, heat the olive oil over medium. Add the fennel, onion and rosemary, and cook for 4 to 6 minutes, stirring occasionally, until tender. Add the garlic and red-pepper flakes and cook until fragrant, about 1 minute.
Add 1/2 pound of Italian sausage, removed from its casing, and cook, breaking it up with a spoon, until browned.
Begin adding handfuls of the greens, cooking and stirring until leaves wilt.
Add the white beans, broth and ¼ teaspoon black pepper, and stir to combine. Bring to a boil, then turn the heat to low and simmer, mashing some of the beans with a wooden spoon, until the liquid has reduced and thickened, 6 to 8 minutes.
Off the heat, stir in the lemon juice, then the mozzarella, if using, and Pecorino Romano. Taste and season with salt and pepper. Divide among shallow bowls and top with more Pecorino Romano. Serve with toasted bread and a dish of red-pepper flakes on the side.