Cook the macaroni according to the package. Drain and rinse with cold water. In the same pot, melt the butter over medium heat. Once melted, add the flour and whisk to thoroughly saturate the flour. Let the roux cook for 1 minute. Slowly add the milk to the pot, whisking constantly. Once the sauce has started to thicken, add the cheese and stir until melted. Add the nutmeg, cayenne pepper, and salt and pepper to taste. Return the noodles to the pot and stir to thoroughly coat. Reduce the temperature to low.

In a medium bowl, mix together with your hands the ground beef, Dijon mustard, steak sauce, and Worcestershire sauce. Form into 4 even patties.

Heat a large cast iron pan or frying pan over medium heat. When hot, add the patties. Cook 4 to 5 minutes then flip. Cook 2 to 3 minutes and add the cheese. Cover the pan and continue to cook an additional 2 to 3 minutes. Remove the lid once the cheese has melted. Set the patties aside and toast the buns in the pan until lightly golden. Spread Boursin cheese on both halves of the buns. Place the burger patty on the bottom bun, top with macaroni and cheese, then place the top half of the bun on. Serve immediately.

Enjoy!