Place a rack in the middle of the oven and preheat it to 200 °C / 390 °F. Line a large baking sheet with parchment paper.
Peel the butternut squash, cut it in half, and remove the seeds. Cut it into 2 cm (1 inch) pieces. Arrange the butternut squash in a single layer over the baking sheet. Add the peeled onion cut into quarters and halved garlic head. Drizzle with olive oil and season with salt and pepper.
bake the squash
Bake the squash in the oven for 45 minutes at 200 °C / 390 °F or until the squash is caramelized and soft. Prepare the rest of the ingredients.
Add butter to the pot, and cook until it starts to foam and smells like nuts. When the butter turns brown, add sage. This will take about 3 - 4 minutes. Pour in the milk and heavy cream. Bring to a boil, then remove from the heat.
Roasted Butternut Squash Soup
Squeeze the baked garlic into the liquid. Add in the baked onion, squash, and water. Remove the sage and mix using an immersion blender (or blender) to get a smooth soup. Divide the Roasted Butternut Squash Soup between six cups and optionally serve with pepitas and a teaspoon of heavy cream.