Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Toss the cubed butternut squash, diced yellow onion, and smashed garlic clove with olive oil, sea salt, and black pepper on the prepared sheet.
Roast the vegetables for 25-30 minutes until the squash is tender and starting to brown at the edges.
While the vegetables roast, season the chicken breast with a pinch of salt and pepper, then bake or pan-sear until it reaches an internal temperature of 165°F.
Place the roasted squash, onion, and garlic into a high-speed blender.
Add the chicken bone broth, fresh sage leaves, and ground nutmeg to the blender.
Blend on high speed until the mixture is completely smooth and creamy.
Dice or shred the cooked chicken breast and stir it directly into the warm soup before serving.