1. Cut the skin off the butternut squash and cut in half lengthwise. Remove the seeds from the inside. Cut the squash into medium sized pieces. Place on baking sheet and toss with olive oil. Season with salt and pepper. Roast at 425° for about 25 minutes, or until tender.
2. Cut off the dark green ends of the leeks. Cut the leeks in half lengthwise and run under cold water to remove any soil. Pat leeks dry. Thinly slice leeks until root end. Add 2 tablespoons butter to a medium sized skillet on low heat, add leeks.
3. Cook leeks on low heat for 20 minutes, adding remaining 2 tablespoons of butter after 10 minutes. Season with salt and pepper.
4. Puree leeks and squash in food processor or with a fork while squeezing the lemon, until smooth.
5. Cook tortellini in salted boiling water according package instructions (approximately 3 minutes for fresh and 8 minutes for dried pasta).
6. Drain pasta and toss with puree. Top with fresh Parmesan and black pepper.
Enjoy!