Melt 4 tablespoons of butter in a large pan over medium heat. Stir in 4 tablespoons of all-purpose flour and cook for about 3 minutes, stirring often. The mixture should look smooth and thick with no raw flour taste.
Stir in 1 teaspoon smoked paprika, 1 teaspoon cayenne pepper, 1/4 cup grated onion, and 1 tablespoon garlic paste. Mix well so the seasonings and aromatics are evenly combined.
Slowly pour in 2 cups heavy cream while stirring. Add 2 cups milk, followed by 12 ounces evaporated milk. Keep stirring until the mixture is smooth and creamy.
Gradually add 16 ounces freshly grated American cheese and 16 ounces freshly grated cheddar cheese. Add the cheese in portions, stirring after each addition until melted and smooth.
Add the cooked al dente elbow pasta and 1 tablespoon Worcestershire sauce. Stir gently until the sauce coats all the pasta evenly.
Grease an oven-safe baking dish. Add half of the macaroni mixture and spread it evenly. Sprinkle grated Monterey Jack over it, then add the remaining macaroni mixture.
Cover the top with grated mozzarella cheese. Sprinkle crushed cheese crackers over the mozzarella, keeping the layer light enough for the cheese to melt properly.
Bake at 350°F for 35 minutes. The macaroni should be hot, the cheese melted, and the cracker topping crisp and golden. Watch the topping near the end so it does not over-brown.
Let the baked macaroni and cheese rest for about 5–10 minutes before serving. This gives the cheese sauce a little time to settle. Scoop it onto plates while it is warm, with the crisp cracker topping on each serving.