Preheat oven to 425°. Line a large baking sheet pan with parchment paper. Arrange cubed butternut squash on the baking sheet, and drizzle with a bit of olive oil. Season with salt and pepper. Keeping the garlic bulb whole, slice off the tips of the cloves, exposing the garlic. Place on a small sheet of foil, drizzle with olive oil, and a pinch of salt and pepper, wrap in the foil and place on the sheet pan with the squash. Roast for 30-40 minutes. If squash cubes are very small, the squash may be done before the garlic. Garlic will take about 40 minutes. Squash should be fork tender, not charred, and garlic fragrant, golden brown, and very soft.
While the squash is roasting, brown the sausage with the yellow onion in a large skillet. Season with sage, Italian seasoning, salt and pepper. Drain excess fat if needed. Keep on low once browned until ready to combine ingredients.
Bring a large pot of salted water to a boil. Cook pasta to al dente or even under, according to box instructions. Reserve 2 cups pasta water.
To a food processor or blender, add roasted squash, garlic, 1/2 cup Parmesan cheese, 1/4 cup ricotta cheese, 1 cup stock, and pinch of salt and pepper. Blend until smooth. Add additional stock to thin it out a bit if needed.
Add cooked pasta and squash mixture to the skillet with the sausage, and bring heat up to medium. Stir to combine. Stir in additional pasta water as needed for consistency. Stir in the other 1/2 cup of fresh grated Parmesan cheese. Taste for seasoning, add salt and pepper as needed.
Serve in bowls with a dollop of whole milk ricotta, a drizzle of prepared basil pesto, and a sprinkle of Parmesan cheese.
Be careful to not overcook your pasta. Undercook by 1-2 minutes, it will finish cooking in the sauce. Any short-cut shape will work nicely. A whole wheat pasta would also be really delicious.