Mix the grated cheddar, Monterey Jack, and gouda cheeses together in a large bowl. Divide the cheese into two separate bowls - half will be added to make the sauce, and half will be sprinkled on top of the mac and cheese layers in the casserole dish.
Preheat oven to 375°F. Lightly grease a 9" x 13" casserole dish.
Bring a large pot of water to a boil. Add a pinch of salt. Once the water is boiling, add the dried pasta and boil until al dente, about 1-2 minutes less than the time stated on the package instructions.
Drain the pasta, but reserve about 2 cups of the pasta water for later.
Make a blonde roux - Melt the half stick of butter in a large skillet over medium heat. Once the butter is melted, whisk in the flour. Cook butter and flour for about 1-2 minutes, whisking often. Then, slowly pour in the milk while whisking constantly to prevent lumps. When all of the milk is added, slowly pour in the half and half, whisking constantly. Continue to heat the roux, whisking often, until a slightly thick and smooth consistency. *Should resemble a thin gravy at this point.
Add ground mustard powder, hot sauce, salt, pepper, and garlic powder to the sauce. Stir to combine.
Remove the skillet from the heat. Stir in the cubed Velveeta until fully melted. If you feel like the sauce is too thick at this point (thicker than a thinned out condensed soup), then stir in ½ to 1 cup of the reserved pasta water. Then add half of the shredded cheeses to the sauce (about 4 cups), and stir well until cheese is melted. *Reserve the remaining cheeses for layering in the casserole dish.
Add the drained pasta to a large bowl. Pour in the prepared cheese sauce, reserving about 1 cup of the sauce. Fold the pasta and sauce together until well combined.
Add about half of the macaroni and cheese mixture to the prepared casserole dish, spreading it out evenly. Then, evenly sprinkle on about half of the reserved shredded cheeses (about 2 cups). Add the rest of the mac and cheese on top of the shredded cheese, spreading it out in an even layer. Then, pour on the remaining 1 cup of cheese sauce. Sprinkle on the remaining shredded cheeses on top (about 2 cups).
Bake the mac and cheese at 375℉ for 15 minutes, or until lightly golden brown and bubbly.