Make the Roux:
Melt the butter in a skillet over medium heat. Whisk in the flour to form a smooth roux. Cook 1–2 minutes until lightly golden and fragrant.
Add Milk & Cream:
Slowly pour in milk while whisking. Add enough to reach a creamy consistency. Add the heavy cream and whisk until smooth.
Add Cheeses to the Sauce:
Remove from heat if needed to prevent curdling. Add a portion of the sharp cheddar and small portions of the Havarti, Gouda, Muenster, Monterey Jack, and Mozzarella. Stir until melted and silky. Season with salt and pepper.
Cook the Pasta:
Boil the elbow noodles just until al dente. Drain but do not rinse.
Prepare the Skillet:
Butter your cast iron skillet generously.
Layer the Mac and Cheese:
Add a layer of cheese sauce, then noodles, repeating until the skillet is filled. Finish with sauce on top. Add the remaining cheddar and small amounts of the other cheeses for a golden crust.
Bake:
Bake at 350°F for 20–25 minutes until bubbly.
Broil:
Turn on the broiler for 1–3 minutes to brown the top. Watch closely.
Cool & Serve:
Let rest a few minutes before cutting to allow the cheese to set.