The key for this stuffing recipe is making your own buttermilk cornbread. This way, you can control the moisture and sugar levels, and it also makes your whole kitchen smell like a buttered corn muffin. Cubing and lightly toasting the cornbread preps it for maximum flavor absorption without compromising its sturdiness.
9 Tbsp. unsalted butter, divided, plus more for pan
2 Tbsp. extra-virgin olive oil
1½ lb. hot or sweet Italian sausage, casings removed
1 large onion, finely chopped
2 celery stalks, finely chopped
6 garlic cloves, thinly sliced
2 Tbsp. finely chopped rosemary
1 Tbsp. kosher salt
½ tsp. crushed red pepper flakes
2 bunches collard greens, stems and ribs removed, leaves torn or cut into 2″ pieces
1½ cups heavy cream
2½ cups low-sodium chicken broth, divided
3 large eggs, beaten to blend
Place a rack in middle of oven; preheat oven to 300°. Cut cornbread into 1″ cubes and divide between 2 large rimmed baking sheets.
Toast, turning over halfway through, until outsides are dried out and some of the sides are golden brown, 45–55 minutes.
Increase oven temperature to 350°. Lightly butter a 13×9″ baking dish. Heat oil in a large Dutch oven or other heavy pot over medium-high. Arrange sausage in a single layer in pot and cook, undisturbed, until browned underneath, about 4 minutes. Break up into bite-size pieces with a heatproof rubber spatula or wooden spoon and continue to cook, tossing occasionally, until just cooked through, about 3 minutes longer. Transfer sausage to a large bowl.
Reduce heat to medium-low and add 8 Tbsp. butter to same pot; swirl to melt and to coat bottom of pot. Add onion, celery, garlic, rosemary, salt, and red pepper flakes. Cook, stirring often, until vegetables are softened but not yet browned, about 5 minutes. Add collard greens and cook, tossing occasionally, until wilted, about 2 minutes.
Add cream and 1 cup broth and bring mixture to a bare simmer. Cover pot and cook until greens are softened, 7–9 minutes.
Add vegetable mixture to bowl with sausage; mix in remaining 1½ cups broth, then eggs.
Add cornbread and carefully toss once (don’t break up pieces). Let sit 5 minutes, then gently toss again.
Let sit until almost all the liquid has been absorbed, about 5 minutes more. Transfer stuffing, still being gentle with it, to prepared baking dish. Dot surface with pieces of remaining 1 Tbsp. butter and cover with foil.
Bake stuffing until hot in the center when pierced with a paring knife, 20–25 minutes. Remove foil and continue to bake until surface is deep golden brown and there are some crispy bits of sausage and greens on top, 25–30 minutes more.
Do Ahead: Cornbread croutons can be made 2 days ahead; store in an airtight container at room temperature. Stuffing can be assembled but not baked one day ahead; cover and chill. Bring to room temperature before baking.