Preheat the oven to 425°F. Fill a large pot 3/4 of the way up with salted water; cover and heat to boiling on high. In a large bowl, whisk together the béchamel, cornstarch, and 1/2 cup of water until combined. Add the cream (shaking the packet before opening) and créme fraîche; stir to combine. In a separate bowl, combine the cheddar and monterey jack blend, fontina, and monterey jack.

Add the pasta to the pot of boiling water. Cook, stirring occasionally, 7 to 9 minutes, or until al dente (still slightly firm to the bite). Turn off the heat. Reserving 1 cup of the pasta cooking water, drain thoroughly. Reserving the pot, transfer the drained pasta to a bowl; drizzle with olive oil and stir to coat.

Meanwhile, place the butter in a medium microwave-safe bowl. Microwave about 30 seconds, or until melted. Add the breadcrumbs, parmesan, as much of the truffle zest as you'd like, and a pinch of salt and pepper. Stir to combine.

To the reserved pot, add the béchamel cream mixture and reserved pasta cooking water; season with salt and pepper. Cook on medium, whisking frequently, 3 to 5 minutes, or until combined and the sauce is slightly thickened. Add the cooked pasta. Cook, stirring frequently, 1 to 2 minutes, or until the pasta is coated and the sauce is thickened. Turn off the heat. Taste, then season with salt and pepper if desired.

Coat a large baking dish with a drizzle of olive oil. Add half the finished pasta to the bottom of the dish. Sprinkle half the cheese mixture over the pasta. Repeat with the remaining finished pasta and remaining cheese mixture. Top with the truffle breadcrumbs in an even layer. Bake 10 to 15 minutes, or until the cheese is melted and the breadcrumbs are toasted. Remove from the oven. Let stand 5 minutes. Enjoy!