Process one 6-oz. package dried stuffing mix (about 2½ cups) in a food processor until the texture of coarse sand, 10–15 seconds. Melt 4 Tbsp. unsalted butter in a large skillet over medium heat. Cook stuffing crumbs, stirring constantly to prevent burning, until golden brown and crisp, 5–7 minutes. Transfer to a plate.

Cook 1 lb. rigatoni, lumache (snail shells), or other medium tubular pasta in a large pot of boiling heavily salted water until al dente, 10–12 minutes for rigatoni or lumache, or 1 minute less than package instructions for other pasta. Drain, reserving 1 cup pasta cooking liquid. Shake colander to remove excess water from pasta; set aside. Reserve pot.

Heat 3 Tbsp. extra-virgin olive oil in reserved pot over medium. Cook 1 lb. sweet Italian sausage, casings removed if needed, breaking up into small pieces and stirring occasionally with a wooden spoon or heatproof rubber spatula, until cooked through and browned, about 5 minutes. Add 6 garlic cloves, finely grated, and ¼ tsp. crushed red pepper flakes and cook, stirring constantly, until garlic is fragrant, about 1 minute.

Add 2 bunches Tuscan kale (about 1½ lb.), ribs and stems removed, leaves torn into 2" pieces, to pot and cook, stirring constantly, until wilted and tender, about 3 minutes. Add reserved pasta and ¼ cup reserved pasta cooking liquid, then add 4 oz. Parmesan, finely grated (about 2 cups), 3 Tbsp. fresh lemon juice, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, 1 tsp. freshly ground pepper, and remaining 5 Tbsp. unsalted butter. Vigorously toss, adding more pasta cooking liquid a little at a time if dry, until cheese is melted and pasta is coated in a glossy sauce. (Don’t be afraid to add more pasta cooking liquid than you think is needed. The pasta will soak it up.) Taste pasta and season with more salt and pepper if needed.

Divide pasta among shallow bowls and top generously with stuffing crumbs and more Parmesan.