1 tablespoon olive oil
1 pound sweet Italian sausage, removed from the casing
1 large onion, chopped
1/4 cup (1/2 stick) unsalted butter
1 small loaf rye bread, roughly torn (about 6 cups)
8 to 10 leaves sage, chopped
1/4 to 1/2 cup chicken stock
Salt and freshly ground black pepper

Place a large skillet over medium-high heat with the oil.  Add the sausage to the pan and cook until golden brown, 7 to 9 minutes.  Using a slotted spoon, transfer the sausage to a paper towel lined plate to drain.  Add the onion to the pan with the sausage drippings, reduce the heat to medium, and cook the onions, stirring occasionally, until caramelized, about 45 minutes.  Reserve with the cooked sausage.

Preheat an oven to 350ºF.

Place the same large skillet back over medium heat with the butter.  Add the bread and sage to the skillet and cook, stirring occasionally, until the bread is toasted and golden brown.  Add the reserved sausage and onions to the skillet along with some chicken stock (make the stuffing as wet as you like it).  Stir to combine and heat through, 3 to 4 minutes.

Transfer the stuffing to a casserole dish and bake in the oven until golden brown on top and heated through, about 20 minutes.  Serve.