preheat the oven to 400°F. heat some water in the large sausepan. add salt and bring to a boil.

add the padta caefully, being careful not to splash. cook the pasta according to package instrustions.

gently melt the butter in a saucepan over low heat. add the flour and mix well. cook the mixture for 1 miinute, than remove from heat.

stir in the milk, a little at a time, to make a smooth sauce. put pan back on heat. stir while the sauce thickens so it doesnt go lumpy.

when the sauce boils, turn down the heat and cook, stirring, for 1-2 minutes. remove from the heat. mix in the chedder, ham, and tomatoes. season.

drain the pasta. mix with the sauce. place in an ovenproof dish and sprinkle with parmesan. bake in oven, on a baking sheet, for 20-25 minutes.