Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes. Drain and set aside.

Melt butter in a large skillet over medium-high heat. Gradually whisk in flour until smooth. Cook and whisk continually for 2 minutes. Add mustard, salt, pepper, cayenne, and garlic; stir to combine. Gradually whisk in half-and-half and milk. Cook, whisking continually, until thickened, 8 to 10 minutes. Add 9 ounces Gouda cheese, chevre, and 1 ounce blue cheese. Stir until smooth. Remove skillet from heat. Stir cooked macaroni into the cheese mixture.

Set an oven rack about 6 inches from the heat source and preheat the oven's broiler.

Divide macaroni and cheese into 6 greased 6-inch cast iron skillets. Top each with corned beef, sauerkraut, Thousand Island dressing, and remaining Gouda and blue cheeses.

Broil skillets in the preheated oven until cheese is golden brown, 3 to 5 minutes.