1. Prepare the Butternut Squash: Preheat your oven to 400 F (200 C). Carefully cut the butternut squash in half lengthwise. Scoop out the seeds and stringy bits with a spoon. Brush the cut sides with 1 tablespoon of olive oil and season lightly with salt and pepper. Place the squash halves cut-side down on a baking sheet.

2. Roast the Squash: Bake the squash for 30-40 minutes, or until it is tender when pierced with a fork. The flesh should be soft enough to easily scoop out, but the skin should still hold its shape.

3. Saute the Aromatics: While the squash is roasting, heat the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add the chopped onion and celery and cook for 5-7 minutes, until softened and translucent.

4. Build the Filling: Stir in the diced apple, chopped fresh sage, and dried thyme into the skillet with the onion and celery. Cook for another 3-5 minutes, allowing the apple to soften slightly and the flavors to meld.

5. Combine with Sourdough: Add the cubed sourdough bread to the skillet. Pour in the vegetable broth and stir well, ensuring the bread cubes absorb the liquid and soften. Season the filling generously with salt and freshly ground black pepper.

6. Stuff the Squash: Once the roasted butternut squash is cool enough to handle, use a spoon to carefully scoop out about half of the cooked flesh from each squash half, leaving a border of about 1/2 inch around the edges to maintain its structure. Mash the scooped-out squash flesh and add it to the skillet with the sourdough filling. Mix everything together thoroughly.

7. Final Bake: Spoon the prepared filling evenly back into the hollowed-out butternut squash halves. Return the stuffed squash to the baking sheet and bake for an additional 10-15 minutes, or until the filling is heated through and slightly golden on top.

8. Serve Warm: Let the stuffed squash rest for a few minutes before serving. This allows the flavors to settle and prevents you from burning your mouth.