Panera's Macaroni and Cheese

2 cups medium shell pasta, uncooked
2 1/2 cups milk
1/2 teaspoon salt
1/4 teaspoon Dijon style mustard
1 tablespoon butter
1 cup grated sharp white cheddar cheese (4 ounces)
1 tablespoon chopped parsley

In a four-quart non-stick saucepan over medium high heat, place dry pasta, milk, salt, and mustard.
Bring to a simmer, stirring frequently over medium low heat until pasta is cooked and sauce has thickened, (about 20-30 minutes).
Remove pan from the heat and stir in the butter and cheese. Garnish with parsley and serve immediately.