First get your macaroni cooking according to the package directions, and get your oven pre-heating to 350.
Next in a sauce pan melt your 1/4 Cup butter, and add your flour. Stir constantly over medium heat until its smooth and bubbly. Continue stirring while you add the milk. Then add in the cream cheese, salt, pepper, and mustard.
When your macaroni is cooked and drained combine it, the sauce, cheddar cheese, all in a well greased casserole dish and stir it up.
Combine the melted butter and bread crumbs in a separate bowl and sprinkle over the mac & cheese.
Pop it into the oven for 20 minutes, until the bread crumbs are nicely browned and the mac and cheese is warm and bubbly!