Preheat the oven to 350°F. Butter a large casserole dish.

Prepare the noodles according to the package directions. Drain, transfer to a large bowl, drizzle with oil, and toss to avoid clumping.

Melt 3 tablespoons of the butter in a large saucepan over medium heat, add the onion, and cook for 5 minutes, or until soft. Add the flour and cook for 1 minute more, stirring. Add 1 cup of milk and stir. As the sauce thickens, add the remaining 1 cup of milk. Bring to a simmer. Add the chicken stock and heat gently for 3 to 4 minutes, stirring constantly. Add the mustard, salt, and pepper, to taste. Add the cheddar cheese, 1 cup at a time, and stir. Add more as it melts. Add the cream cheese and stir until melted.

Pour the sauce over the noodles and stir to coat. Transfer the mixture to the casserole dish. Sprinkle with cracker crumbs to cover evenly.

Melt the remaining 3 tablespoons of butter in a pan over low heat and drizzle over the crumbs. Bake at 350°F for 30 to 35 minutes, or until bubbly.

Super-Creamy Mac and Cheese Variations:

Bacon Mac and Cheese: Add 4 to 5 slices of crisp-cooked, crumbled bacon to the noodles when you add the sauce. Continue as directed.

Pepperoni Pizza Mac and Cheese: Add ⅓ cup of chopped pepperoni slices to the noodles when you add the sauce. Instead of cracker crumbs, cover with sliced tomatoes and additional shredded cheese. Bake as directed.