Warm the olive oil in a small skillet over medium heat. Add the garlic and sauté until tender and starting to turn golden, about 2 to 3 minutes.
Pour the half and half into a blender. Add the butternut squash, the chicken stock, and the garlic.
Purée, starting on low speed using the tamper if needed. Blend, turning the speed up to medium until the squash is very smooth and blended into the chicken stock and half and half, about 1 to 2 minutes.
Add the sage, marjoram, thyme, kosher salt, and black pepper. Blend into the sauce on medium speed, about 30 seconds.
Transfer the sauce to a saucepan and warm over medium heat, about 15 to 20 minutes.
While the sauce warms, cook the tortellini in a large pot of boiling, salted water until just tender.
Toss the hot pasta with the butternut squash sauce and garnish with a sprinkling of Parmesan cheese and toasted pecans.
To roast the butternut squash:
Scoop the seeds out of each half of the squash and place them cut side up on a baking sheet lined with parchment paper. Brush each half with the olive oil then sprinkle with salt and pepper. Place a teaspoon of butter in the cavity of each side.
Roast in a 400-degree oven for about 1 hour or until the squash is tender when pierced with a sharp knife.