Preheat the oven to 425°F (220°C).
Cut the butternut squash in half lengthwise and scoop out the seeds. Place it on a baking sheet, cut side up, and roast for 25-30 minutes or until tender.
Wrap the garlic cloves in foil and roast them in the oven for 20-25 minutes or until soft.
Peel and chop the roasted squash into cubes.
Cook the rotini pasta according to package instructions until al dente. Reserve 1 cup of starchy pasta water before draining.
In a blender or food processor, combine the roasted squash, garlic, cashews, water, sage, nutmeg, thyme, balsamic vinegar, salt, and pepper. Blend until smooth.
In a large skillet, heat the olive oil over medium heat. Add the blended squash mixture and cook for 2-3 minutes, stirring constantly.
Add the reserved pasta water to the skillet and stir to combine. Bring the mixture to a simmer and let cook for 2-3 minutes or until the sauce has thickened slightly.
Add the cooked rotini pasta to the skillet, tossing to coat with the squash sauce.
Serve hot, garnished with additional thyme if desired.