4 tablespoons unsalted butter, plus more for greasing
1 pound sweet Italian fennel sausage, casings removed, broken into small pieces
3 large leeks, white and light-green parts only, sliced
1/2 medium butternut squash, peeled and diced
Kosher salt and freshly ground pepper
1 bunch kale, leaves trimmed and chopped
1 pound stale onion focaccia, cubed
1 large egg
2 cups low-sodium chicken broth or turkey stock
1 cup diced parmesan cheese, plus 1/4 cup shredded
Preheat the oven to 350 degrees F. Butter a 3-quart casserole dish. Heat 1 tablespoon butter in a large Dutch oven or heavy pot over medium heat. Add the sausage and cook until golden brown, about 6 minutes. Add the leeks and squash and season with 1 teaspoon each salt and pepper; cook until the leeks are soft, about 3 minutes. Add the kale, toss and cover until the kale wilts, about 4 minutes. Add the focaccia cubes and the remaining 3 tablespoons butter and toss until the butter melts.
Whisk the egg and chicken broth in a bowl until smooth; stir in the diced Parmesan and 1 teaspoon salt. Pour the broth mixture over the bread mixture; cook until the liquid is absorbed by the bread, about 1 minute. Transfer the bread mixture to the prepared casserole dish. Scatter the shredded cheese evenly on top and bake until golden and cooked through, about 40 minutes. Set aside for 5 minutes before serving.