Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
In a large saucepan over medium heat, melt butter. Saute garlic 30 seconds. Whisk in flour, salt and pepper. Cook and stir until smooth. Pour in milk, a little at a time, stirring constantly. Bring to a boil for 1 minute. Stir in mustard and cheese. Continue to cook, stirring occasionally until cheese is melted. Remove from heat and stir in pasta and ham.