Preheat the oven to 425°F.
Cut the butternut squash in half vertically. Scoop out seeds and pulp with a large spoon. Using a peeler, remove skin and white flesh below. You can leave the stem intact or off.
Brush the squash with olive oil then season with salt and pepper. Roast for about 15 minutes. Remove from the oven and use a sharp knife and carefully slice the flesh into thin slices. Cut as deep as you can without cutting all the way through. This keeps the squash intact.
In a medium saucepan, add butter, sage, rosemary, apple cider vinegar, and maple syrup over medium-high heat. Cook for about 5 minutes. Be sure to keep stirring to prevent burning.
Use a brush to spread the glaze all over the squash, then transfer the Hasselback squash to the oven, cook and basting every 15 minutes. Repeat this process until the squash is cooked through and tender for another 30 minutes or longer.
Optional: Add some fresh sage leaves to the baking sheet for about 3-5 minutes before the cooking is done.
Remove from the oven. Serve topped with shredded parmesan cheese, bacon bits, walnut pieces and browned butter sage leaves.