1. Preheat oven to 400°.
2. Bring 8 cups water to a boil in a large saucepan; add cauliflower and 1/2 teaspoon salt to boiling water, and cook 4 minutes or until tender. Remove cauliflower with a slotted spoon to a large bowl, reserving cooking liquid; set cauliflower aside. Bring cooking liquid to a rolling boil. Add pasta, and cook 6 minutes or until al dente; drain and add to cauliflower in bowl.
3. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and milk in a medium saucepan, stirring well with a whisk. Stir in garlic; cook over medium-high heat until thick (about 8 minutes), stirring frequently. Remove from heat; stir in remaining 1/4 teaspoon salt, cheeses, mustard, and pepper. Pour cheese sauce over cauliflower mixture; add ham, stirring to coat. Spoon cauliflower mixture into a 13 x 9inch glass or ceramic baking dish coated with cooking spray.
4. Tear bread slices into quarters. Place bread in food processor; pulse 10 times or until coarse crumbs form to measure 1 cup. Combine breadcrumbs with butter; sprinkle evenly over cauliflower mixture. Bake at 400° for 20 minutes or until lightly browned.
Young Chefs can:
Break cauliflower into small pieces, and place in measuring cups
Tear bread slices into quarters
Older Chefs can:
Dice ham with dinner knife
Sprinkle breadcrumb mixture