I am from the South, and I have never had macaroni and cheese with tomatoes either???? Macaroni and cheese, or macaroni with tomatoes, but not both together.
Macaroni and and cheese is very easy.
cook your macaroni until done, but not super mushy. (you don't want it to make 'mush' when you stir it all together.
Choose the cheeses that you like, you just have to be sure that the cheeses are the kind that melt. (some do not melt as well) Some like a sharp cheese, some like velveeta, some like mild cheddars or even american. Any cheeses that will melt well would be great.
Put a little milk, butter, and salt in a pot. (flour and pepper are optional)
As this heats, add twice as much cheese as you think you need!!!
Then add your macaroni.
Taste to make sure it has enough salt. (usually needs a bit more than you think) the amount of salt might depend on how salty your cheeses are.
Heat just until it starts to come to boil and the cheese starts to get melty. Do not overcook!
If you want to add tomatoes, I would probably dice and drain some canned tomatoes very well. They should probably be almost dry???? And then fold them in very carefully.
For those who want to make it into a casserole, just pour it all into a baking dish, top with more shredded cheese, and bake in a hot oven for a few minutes.