Preheat the oven to 375 ̊ F. Stir the butter and flour in a small bowl to make a paste. Cook the bacon in a large skillet over medium-high heat until crisp, about 10 minutes. Remove the bacon to a paper towel–lined plate. Pour off all but 2 tablespoons fat from the skillet.
Add the onion to the skillet and cook until softened, about 4 minutes. Add the garlic, parsley, sage and Italian seasoning and cook until the garlic is softened, about 1 minute. Season with 1 teaspoon each salt and pepper. Stir in the milk and heavy cream; bring to a simmer. Whisk in the butter-flour paste and cook until thickened, about 6 minutes. Remove from the heat; stir in 1/2 cup Parmesan and the bacon.
Combine the mozzarella and fontina in a bowl. Spread 1/2 cup of the cream sauce on the bottom of a 9-by-13-inch baking dish; top with 3 lasagna noodles. Top with a layer of butternut squash slices, overlapping them, then 1/2 cup more sauce and 1/3 cup mozzarella-fontina mixture. Repeat the layering 5 more times (noodles, squash, sauce, cheese), using up all the squash. Top with the remaining 3 noodles, then the remaining sauce and mozzarella-fontina mixture. Cover with foil and bake until the squash is tender, 35 to 40 minutes.
Mix the breadcrumbs and remaining 1/4 cup Parmesan; sprinkle over the lasagna. Bake, uncovered, until golden, 15 minutes. Let sit 10 minutes before serving.