Melt butter in a Dutch oven over medium heat; add garlic, and saut until tender.
Add milk, and cook until thoroughly heated. Gradually stir in 1/2 cup Parmesan cheese and next 6 ingredients until smooth. Stir in spinach, if desired.
Add pasta, tossing to coat; spoon into a lightly greased 13- x 9-inch baking dish.
Bake at 400 for 7 minutes.
Remove from oven; sprinkle with remaining 1/2 cup Parmesan cheese and breadcrumbs. Reduce oven temperature to 35