Add the butter to a medium skillet over medium heat, stir in the diced onion and cook-- stirring occassionally-- until the onions are beginning to brown.
In a large bowl, add the pasta, soup, cheeses, broccoli, mayonnaise, milk, onion, garlic, half of the bacon, smoked paprika, salt, and pepper. Stir everything together, just until evenly combined.
Spray a 9x13 baking dish with non-stick cooking spray. Pour the mac and cheese into the pan and use a spatula to smooth it out into an even layer. Sprinkle the chipotle powder and the remaining bacon evenly out over the top of the macaroni.
Bake the mac & cheese at 350 degrees for 30 minutes.