Cook the pasta in salted water until just shy of al dente (about 1 1/2 to 2 minutes less than package directions). Drain and set aside.
Make cheese sauce/bechamel sauce: In a large pot, melt the butter over medium heat. Whisk in flour and cook for about 1 to 2 minutes, until golden. Gradually whisk in the room temperature milk until smooth and it begins to thicken. Add mustard powder and garlic powder.
Add cheeses: Remove the pot from the heat and gradually stir in the shredded cheddar and Gouda until melted and smooth, then stir in the cream cheese. Season with salt and pepper.
Combine: Fold in cooked pasta until fully combined with no dry spots, then incorporate the chopped lamb until evenly distributed.
Transfer to pan: Spoon mixture into a greased 13x9 pan, cast iron skillet, or Dutch oven. You can even make it in mini cast iron skillets for individual servings.
Make the crunchy topping: Melt the butter in a small skillet, stir in the panko, smoked paprika, and salt until golden. Sprinkle evenly over mac and cheese.
Bake in the oven or smoker for about 20 to 25 minutes until it starts to bubble and is crunchy and golden on top.
Rest for 5 minutes before serving.
Video
Notes
To make smoked lamb shoulder: Salt a 3 lb American lamb shoulder overnight, rub with black pepper, smoked paprika, and crushed rosemary, then smoke at 250°F until internal temperature reaches 200-204°F (5-6 hours). Wrap and rest 30 minutes before shredding. For complete smoking instructions and pro tips, see our detailed smoked lamb shoulder guide.
Make-Ahead Instructions: Assemble the mac and cheese completely through step 7 (topping step), then cover tightly and refrigerate. When ready to serve, bake directly from the refrigerator, adding 10 to 15 extra minutes to the cooking time since it's starting cold. The dish is done when bubbly around the edges and golden on top.
**The USDA recommends an internal temperature of 145°F, with a 3 minute rest.