Now with BACON!
1/2 cup (1 stick) unsalted butter, divided
1/4 cup all-purpose flour
3 cups whole milk
3 cups water
1/2 pound crispy roasted bacon cut into bits, divided
1 teaspoon kosher salt plus more
1/2 teaspoon freshly ground black pepper plus more
1 pound elbow macaroni
2 cups shredded cheddar, divided
2 garlic cloves, chopped
1 cup panko (Japanese breadcrumbs)
Preheat oven to 400°F. Melt 1/4 cup butter in a large saucepan over medium-high heat. Add flour; cook, whisking constantly, for 1 minute. Whisk in milk and 3 cups water. Bring to a boil, reduce heat to a simmer, and cook, whisking often, until a very thin, glossy sauce forms, about 10 minutes. Stir in 1 teaspoon salt and 1/2 teaspoon pepper. Remove sauce from heat.
Toss pasta, 1/2 of the bacon and 1 1/2 cups cheese in a 13x9x2" or other shallow 3-quart baking dish. Pour sauce over (pasta should be submerged; do not stir) and cover with foil. Bake until pasta is almost tender, about 20 minutes.
Meanwhile, melt remaining 1/4 cup butter in a large skillet over medium heat. Add garlic, panko, remaining bacon, and toss to combine. Continue heating until panko takes on golden brown color. Season with salt and pepper.
Remove foil from dish. Sprinkle with remaining 1/2 cup cheese, then panko mixture. Bake until pasta is tender, edges are bubbling, and top is golden brown, about 10 minutes longer. Let sit 10 minutes before serving.