Cook Pasta: In a large saucepan, bring a pot of water to a boil, then boil 8 ounces uncooked elbow macaroni until al dente. Drain and rinse with cold water, then set aside. If using leftover plain pasta, measure out about 3 cups and make sure it’s fully cooled before using.
Make Cheese Sauce: Melt 2 Tablespoons salted butter in a pot over medium heat. Sprinkle 2 ½ Tablespoons all-purpose flour over butter and cook for 2 minutes, stirring constantly, to form a roux. Slowly whisk in 1 cup whole milk, then add 1 ½ teaspoons Kosher salt, ½ teaspoon black pepper, ½ teaspoon onion powder, ½ teaspoon garlic powder, and ¼ teaspoon paprika. Cook until thickened. Add 3 cups shredded cheddar cheese, a handful at a time, stirring until smooth before adding more.
Combine and Set: Add cooked pasta to sauce and stir until evenly coated. If mixture looks loose, cook for a few more minutes until thick. Spread evenly into a parchment-lined 9x9-inch pan, cover, and refrigerate for at least 4 hours or overnight.
Cut and Coat: Once firm, remove mac and cheese from the pan and cut into 36 squares. Set up three bowls: in first bowl, mix 1 cup all-purpose flour, 1 teaspoon Kosher salt, and ½ teaspoon coarse ground pepper. In second bowl, whisk together 2 large eggs and 2 Tablespoons milk. In third bowl, combine 2 cups panko breadcrumbs and 1 teaspoon dried parsley flakes. Coat each square in flour mixture, then dip in egg mixture, and finish in panko mixture. Place on a parchment-lined baking sheet and freeze for 10 minutes.
Fry: Heat 3 inches of oil in a heavy pot to about 365 °F. Fry a few bites at a time until golden brown, about 2-3 minutes. Use a slotted spoon to transfer the bites to a paper towel-lined plate to remove excess grease. Repeat with the remaining bites.
Serve: Sprinkle with parsley if using. Serve on their own or with dipping sauces.