MAKE THE CRUMB TOPPING. In a small skillet, melt the butter over medium heat.
Add the garlic and a pinch of salt, and cook until fragrant, about 1 minute.
Add the panko and cook, stirring constantly, until golden brown, about 5 minutes. Transfer immediately to a bowl; cool completely.
MAKE THE MAC & CHEESE. In a large bowl, toss the cheddar, Monterey Jack, Colby and flour and toss until the cheese is fully coated.
Meanwhile, in a large saucepan, melt the butter over medium heat.
Add the shallots and cook until softened, about 5 minutes.
Add the garlic and cook until fragrant, about 1 minute more.
Add the paprika, Worcestershire, Dijon and pepper and stir to combine.
Add the milk and increase the heat to medium-high; cook , stirring often, until the milk begins to steam.
Add the cheese mixture and bring to a boil, stirring constantly until the cheese is melted and the sauce has thickened, for 2 minutes.
Season with salt, to taste, if necessary.
Add the pasta and mix to combine.
Add up to ¼ cup of the reserved pasta water to control the creaminess of the sauce; serve immediately.