This is comfort food with a luxurious twist.
Bring a large pot of water to a boil for the pasta.
Invert a small bowl inside a large bowl. Stand 1 ear of corn on the small bowl. Using a sharp knife, cut off the kernels. Use the flat edge of the knife to scrape the juices from the cob. Repeat with the remaining ears of corn.
In a large skillet, melt 2 tbsp. butter over medium-high heat. When it foams, add the scallions, celery, chiles, thyme, garlic, bay leaf, and corn; season with salt and pepper. Cook, stirring often, until the vegetables soften, 5 to 6 minutes. Stir in the crabmeat, Old Bay, and hot sauce.
Salt the boiling water and add the pasta. Cook until 1 minute shy of the package directions.
In a large bowl, toss both cheeses with the cornstarch. Stir in the evaporated milk.
Drain the pasta and return it to the pot. Add the remaining 2 tbsp. butter and the cheeses. Toss the pasta over medium heat until the cheeses melt and the sauce is blended, 1 to 2 minutes. Mix in the vegetables and crabmeat; season.
Stovetop mac and cheese is the way to go. The pasta stays firmer and moister than the baked version.