In large skillet, fry bacon until crispy.
Remove from skillet, and set aside, keeping about 2 tablespoon of bacon grease in skillet. (If not using bacon, just heat 2 tablespoon of olive oil in large skillet)
Add shallots and cook over medium heat for 1 minute.
Add butternut squash and sage and cook over medium heat for 10-12 minutes, until squash is tender. I covered the squash for about 5 minutes to let it "steam."
Place squash in large bowl and mash with a potato masher.
Mix in ricotta cheese, milk, salt, pepper, and diced bacon. Set aside.
This would be a good time to cook the lasagna. Once cooked, keep the noodles in a large bowl of cold water to keep them from sticking to each other.