Baked Mac and Cheese Steak Casserole is the perfect oozy and cheesy comfort food with a little added flavor from the steak and sauteed onions.
Preheat oven to 350.
Cook pasta for 3 minutes, drain well.
In a medium saucepan, melt butter. Stir in flour to make a roux and add in mustard, salt and pepper.
Gradually add milk and cook until mixture is smooth and bubbly, stirring constantly.
Cook over medium heat until mixture boils, stirring constantly.
Turn heat to low and simmer 1 minute, stirring constantly.
Gradually mix in cheddar cheese, and stir until cheese is melted.
In a separate pan, cook thinly sliced steak and sautee onions in olive oil.
Combine pasta to cheese sauce and mix lightly. Add in sauteed onions and cooked steak and mix until combined.
Top with additional cheese, croutons or breading (if desired). Bake uncovered for 25 minutes or until internal temperature reaches 165 to 175.
Remove from oven and allow to cool slightly before slicing and serving.