Bake the squash for puree (optional)
Preheat the fan-assisted oven to 210 °C / 410 °F. Peel the butternut squash. Remove the seeds and cut the squash into small 1cm x 1cm (1/2-inch x 1/2-inch) cubes. Line a large baking sheet with parchment paper. Arrange the squash on top and place it in the preheated oven. Bake for 30 - 35 minutes at 210 °C / 410 °F or until the squash is soft. Don't over-bake the squash. Remove from the oven and set aside to cool to room temperature. Or use store-bought pumpkin puree.
make the puree for the sauce
Combine 150g (5.3 ounces) pumpkin puree or homemade squash puree, peeled garlic, milk, and butter in a blender. Mix into a smooth mixture. Season with salt and pepper.
cook the tortellini
Cook the Cheese tortellini according to the package instructions. Before draining, remove 120ml (1/2 cup) of the pasta cooking water, then drain.
butter and sage
Add butter to a large pan and place over medium-high heat. When the butter starts to foam, add the sage. Pan-fry for 1 - 2 minutes or until the sage is crispy. Remove from the pan and transfer to a plate lined with a paper towel. Continue to cook the butter until light brown.
Add the tortellini to the butter and cook for about 30 seconds, then add the prepared pumpkin puree, 80ml (1/3 cup) of pasta water, and grated parmesan cheese. Toss to combine, then divide between four plates. Serve with crispy sage and additional grated parmesan, if desired.TipAdd all the pasta water to get a creamy, luscious sauce, if needed.