Super creamy and delicious!
Adjust oven rack to upper-middle position and heat oven to 375° Bring 4 quarts water to boil in Dutch oven. Add macaroni and 1 tablespoon salt. Cook for 5 minutes. Drain macaroni; set aside.
Add butter to now empty pot and melt over medium-high heat. Stir in flour, mustard, 3/4 teaspoon pepper, and 1/2 teaspoon salt. Cook until mixture is fragrant and bubbling, about 30 minutes. Slowly whisk in milk and cream. Bring to a boil. Reduce heat to medium-low and simmer until sauce is thick enough to coat back of spoon, about 2 minutes, whisking frequently.
Remove pot from heat. Add 2 cups sharp cheddar cheese and 2 cups Gouda cheese, cream cheese or sour cream, hot sauce, Worcestershire sauce and whisk until cheese is melted. Add pimentos and macaroni. Stir until macaroni is thoroughly coated in sauce. Transfer to a 13 x 9-inch baking dish. Sprinkle with remaining 1/2 cup cheddar cheese and 1/2 cup Gouda.
Bake until edges are lightly browned and filling is bubbly, 25 to 35 minutes. Let rest 10 minutes before serving.