Step 1

Preheat oven to 350℉ and adjust oven rack to upper third of oven. Bring large pot of water to a rolling boil. Season water with one tablespoon of kosher salt. Cook pasta according to package directions, drain and set aside.

Step 2

In same pot, melt butter over medium heat. Once butter is melted, sprinkle in flour and let cook for 1-2 minutes, stirring constantly. Slowly whisk in warmed milk and evaporated milk and let come to a simmer. Stir often to prevent scorching. Once the béchamel sauce has started to thicken remove from heat and stir in cheddar cheese, parmesan cheese, and 1/2 of Colby-jack cheese, one handful at a time letting the cheeses melt in between handfuls. IMPORTANT - The béchamel sauce should still be warm but not be bubbling when the cheese is added. If the sauce is too hot the cheese with seize up and become stringy instead of melting. Having the shredded cheese at room temperature helps it melt quicker.

Step 3

Season cheese sauce with 1/2 teaspoon kosher salt and freshly ground black pepper. Mix in mustard. Stir in pasta and taste for seasoning and adjust as needed.

Step 4

Transfer pasta to 9x13 baking dish and top with remaining colby-jack. Bake uncovered for about twenty minutes, or until heated through and edges have started to bubble. Remove macaroni and cheese from oven and turn broiler on high. Once broiler has preheated, return mac and cheese to oven and let cheese broil. Watch carefully and only let broil for 1-2 minutes to prevent mac and cheese from getting too hot. See recipe notes below. Top mac and cheese with fresh chives.