Preheat oven to 350 degrees F. Boil water and prepare pasta according to directions, shaving 1-2 minutes off of cooking time. I cooked my fettuccine for 6 minutes.
Heat a large saucepan over medium heat and add butter. Once sizzling, whisk in flour and stir to create a roux, until bubbly and golden, about 4-5 minutes. Add garlic and cook for 30 seconds. Add in milk, stirring constantly and increasing heat a little bit until it begins to bubble and thicken, about 5-6 minutes. Add in mascarpone, parmesan, pumpkin, sage, salt, pepper and pumpkin pie spice, mixing well until smooth and combined and thickened into a sauce.
Spray a baking dish (mine was 7×11) with nonstick spray and add pasta to the dish. Pour sauce over top and toss well with kitchen tongs to coat. Add some grated fontina on top and a sprinkling of bread crumbs. Bake for 15-20 minutes, until bubbly and slightly golden.
While pasta is baking, heat a small saucepan over medium heat and add olive oil. Once hot, add sage leaves 4-5 at a time and fry for about 30 seconds. Remove and place on a paper towel.
Serve pasta immediately and top with sage leaves.
[This can easily be reheated but like any alfredo, you will need to add a bit of milk or liquid as it warms to bring the creaminess back to the dish.]