Boil macaroni as per instructions on packet, drain and put aside.
For cheese sauce, put the butter, flour and milk in a pan. Stir constantly over gentle heat until boiling. Reduce heat and cook for 5 minutes. Add the 55g to 85g grated cheese and mustard. Season with salt and pepper.
Add cooked macaroni to pan. Put mixture into baking dish, sprinkle with remaining 30g cheese.
Bake in the preheated oven for 15 minutes.
Add sliced tomatoes before baking, sprinkle with paprika.