Preheat the oven to 350 degrees F. Butter a shallow 3 quart baking dish. Set aside.
Place the brioche and sourdough bread pieces in a large bowl. Using a large sauté pan, heat the olive oil over medium-high heat. Add the sausage- breaking up with a wooden spoon- and cook until browned, about 8-10 minutes. Using a slotted spoon, transfer the sausage to the bread bowl.
Next, add the onion, celery, and fennel to the hot sauté pan. Sprinkle generously with kosher salt and freshly ground black pepper. Cook until the vegetables have softened, about 10-12 minutes, and then add to the bread bowl.
Add the wine to the hot skillet, scraping up the browned bits on the bottom of the pan while the wine reduces by half. Once reduced, add the chicken stock, maple syrup, and 1/2 cup butter. Cook until the butter melts. Pour this mixture over the bread.
Toss all of the ingredients together until the bread has absorbed the liquid and is hydrated. If it appears to be dry, simply add 1/4 cup chicken stock at a time.
Taste the stuffing, adding a pinch or two of salt and pepper if needed.
Transfer the bread mixture to the prepared, buttered baking dish.
Cover with a buttered piece of foil and bake until a pairing knife inserted in the center comes out clean and hot, about 30 minutes. Increase oven temperature to 400 degrees F and bake with foil removed until the top is golden brown and crisp, about 20 minutes.
Allow the stuffing to sit for about 10 minutes before serving.
Garnish with spiced pepitas and dig in!