Step 1: In a medium saucepan, melt the butter over medium heat. Add the flour and whisk constantly for 1–2 minutes to form a roux.Step 2: Gradually pour in the milk and heavy cream while whisking continuously. Cook for about 4–5 minutes until the mixture thickens slightly.Step 3: Reduce the heat to low and slowly add the shredded cheddar cheese, Gruyère cheese, and cream cheese. Stir continuously until the cheese is fully melted and the sauce becomes smooth.Step 4: Add mustard powder, garlic powder, salt, black pepper, and paprika. Stir well and adjust seasoning to taste.Step 5: Cook pasta separately according to package instructions, drain, and pour the cheese sauce over the hot pasta. Stir until the pasta is evenly coated with the creamy cheese sauce.Step 6 (Optional): For baked mac and cheese, transfer the pasta and sauce mixture to a greased baking dish, top with shredded cheese and breadcrumbs, and bake at 375°F (190°C) for 20 minutes until golden and bubbly.