Bring a large pot of generously salted water to a rolling boil, then add the elbow macaroni and cook for 2 minutes longer than the package maximum time. Drain in a colander, rinse briefly with cold water, and set aside.
Preheat the oven to 350°F (175°C). Grease a 9x13-inch (23x33cm) baking dish with butter or nonstick spray and set it on a rimmed baking sheet.
In a large bowl, whisk together the eggs, evaporated milk, whole milk, sour cream, salt, black pepper, garlic powder, onion powder, smoked paprika, dry mustard, and hot sauce until fully combined and smooth.
Transfer the drained macaroni to the prepared baking dish, then scatter the cubed Velveeta, 1.5 cups of the sharp cheddar, all of the Colby Jack, and the butter pieces evenly over and through the pasta. Toss gently with a spatula to distribute.
Pour the custard mixture slowly and evenly over the pasta, then press down gently with a spatula so the macaroni is mostly submerged. Let it sit for 2 to 3 minutes to settle.
Mix the remaining 0.5 cup sharp cheddar with the mild cheddar and sprinkle evenly over the top, then bake uncovered at 350°F (175°C) for 40 to 45 minutes, until the top is golden brown and the center is just set with a slight jiggle.
Remove from the oven and let the mac and cheese rest for at least 10 minutes before serving so the custard fully sets and portions scoop cleanly.