In a large pot of boiling salted water, cook pasta according to package instructions; drain well.
Run cold water over the pasta to remove starches so it doesn't get stuck together while you cook the rest of the dish.
Melt 6 tablespoons butter in the skillet over low heat, until the butter starts to foam. Pour browned butter into a small bowl and set aside.
Melt 2 tablespoons butter in the skillet over medium heat. Add butternut squash and cook, stirring occasionally, until golden brown and tender, about 12 minutes.
Add pecans and spinach and cook until spinach is wilted. (2-3 more minutes.)
Add garlic to the skillet, and cook, stirring until fragrant. Stir in pasta, butternut squash, spinach and pecans, and the browned butter. Stir until well combined.
Serve immediately, garnished with Parmesan and chopped fresh parsley, if desired.