Kosher salt
4 ounces elbow macaroni (1 cup)
Cooking spray
2 plum tomatoes, sliced 1/2 inch thick
4 1/2-inch-thick slices baguette
Freshly ground pepper
3 shallots
1 carrot, cut into 1-inch pieces
1 stalk celery, cut into 1-inch pieces
1/4 cup all-purpose flour
3 3/4 cups fat-free low-sodium chicken broth
1 1/4 cups 2% milk
6 ounces shredded cheddar cheese (about 1 1/2 cups)
1/4 cup grated parmesan cheese