Preheat your smoker to 225°F (107°C).
Cook the pasta, Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package instructions for al dente. Drain the pasta and set it aside.
Make the cheese sauce in a large saucepan over medium heat, melt the butter. Whisk in the flour and cook for 1 minute, stirring constantly, to form a roux. Slowly whisk in the milk and heavy cream, bringing the mixture to a simmer. Reduce heat and simmer for 5 minutes, or until slightly thickened.
Add the cheese & Remove the pan from heat and gradually whisk in the shredded cheddar, Gruyere, and Monterey Jack cheeses until melted and smooth. Stir in the Dijon mustard, smoked paprika, garlic powder, salt, and pepper.
Combine in a large bowl, toss the cooked pasta with the cheese sauce until evenly coated.
Transfer the mac and cheese to a baking dish suitable for smoking. A cast iron skillet or a ceramic dish work well.
Smoke the mac and cheese. Place the dish on your smoker and smoke for 1 hour, or until the top is golden brown and bubbly.
Serve immediately. If desired, top with panko breadcrumbs that have been toasted in melted butter for a crispy finish, and garnish with chopped fresh chives.