Preheat the oven to 350, and butter a casserole dish.
In a saucepan, heat the two tablespoons butter until foamy. Sprinkle in the flour and whisk until it turns golden, then slowly pour in the milk, continuing to whisk.
Bring to a simmer over medium heat and let it thicken.
Stir in the cheese and remove from the heat (it should be a loose sauce). Fold in the macaroni, then add tomatoes by squeezing them between your fingers. The mixture should be loose like a thin batter; if it's gluey or thick, add a little milk or drained tomato juice.
Pour into the casserole dish and spread breadcrumbs over the surface. Top with 1/4 cup cheese and ground pepper. Bake until browned on the top and bubbling, about 25 minutes.