Preheat oven to 375 degrees F. Grate cheeses, placing them together in a large bowl. Boil water and prepare pasta according to directions, cooking for 3-4 minutes less than called-for time.
Heat a large oven-safe skillet over medium heat. Once hot, add in olive oil and butter, then throw in shallots with a pinch of salt. Stir to coat and cook for 2-3 minutes, until soft. Add in garlic and cook for 30 seconds. Add flour to the skillet then whisk constantly to create a roux. Let cook for 2-3 minutes until golden brown. Pour in milk, stirring continuously for another 1-2 minutes. Add in mascarpone and almost all of the grated cheeses, reserving about 1/2 cup of the grated cheese. Stir continuously until mixture thickens, about 3-4 minutes. Season with salt, pepper and nutmeg, then tasted and season more if desired. Add pasta to the skillet and toss thoroughly to coat.
Sprinkle the top of the mixture with remaining cheeses and breadcrumbs. Bake for 30-35 minutes, or until top is golden brown and bubbly. Serve immediately.
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