Kosher salt, to taste
8 oz. hollow pasta, preferably elbow macaroni or shells
3 slices crustless white bread
6 tbsp. unsalted butter
½ tsp. paprika
3 sprigs fresh thyme
2 shallots, minced
1 bay leaf
¼ cup flour
⅛ tsp. cayenne pepper
3 cups milk
10 oz. grated sharp white cheddar (about 4 cups)
10 oz. grated Gruyère (about 4 cups)
6 oz. Velveeta, cut into ½” cubes (about 1¼ cups)
1 oz. blue cheese, crumbled (about ¼ cup)
Freshly ground black pepper, to taste
1. Heat oven to 375°. Bring a 4-qt. saucepan of lightly salted water to a boil. Add pasta and cook, stirring occasionally, until cooked halfway through, about 3 minutes for elbow macaroni. Drain pasta; set pasta aside. Tear bread into small pieces and transfer to the bowl of a food processor. Process until finely ground; set aside. Return pan to medium heat and melt 3 tbsp. butter. Add bread crumbs and stir to combine. Transfer bread crumb mixture to a plate and set aside.
2. Wipe out pan and set over medium heat. Melt the remaining butter and add the paprika, thyme, shallots, and bay leaf; cook, stirring often, until shallots are soft, about 5 minutes. Add flour and cayenne and stir until mixture thickens, 1 minute. Whisk in milk and cook, continuing to whisk often, until sauce has thickened and coats the back of a spoon, about 10 minutes. Discard thyme and bay leaf and remove pan from heat.
3. Stir in cheddar, half the Gruyère, the Velveeta, and the blue cheese; continue stirring until smooth. Stir in pasta and season sauce with salt and pepper. Transfer mixture to an 8″ x 8″ baking dish. Sprinkle remaining Gruyère over top of pasta and then top with bread crumbs.
4. Transfer baking dish to an aluminum foil-lined baking sheet and bake until macaroni and cheese is golden brown and bubbly, 30 minutes. Let cool for 10 minutes before serving.