Sweet Onion Mac and Cheese

Bring a pot of water with the sea salt to a boil over high heat. Add the pasta and cook according to your package instructions then drain well.

While the pasta is cooking, add the butter to a large sauté pan, over medium-high heat. Add the onions, when the butter is melted. Cook for 5 minutes, and then lower the heat to medium. Cook for 5 minutes, and then lower the heat to low. Add the balsamic vinegar, stir, sprinkle with the flour, stir again, and increase the temperature to medium-high. Cook for 3 minutes, stirring often.

Whisk in the milk, pepper, salt, and mustard. Cook for 10 minutes, stirring often. Whisk in the cheese and cook for an additional 2 minutes.

Combine the sauce with the drained pasta and serve immediately.