Cheddar Fish, but not Goldfish

Last night, the little boys were sick. Sleep all day, sneeze a little, cough a lot, leave poor Thor lonely...you get the picture. Anyway, dinner needed to be fast and easy so I could get my sickos back to bed. This fish was fast and easy, and everyone liked it. There's not much of a recipe here; it was more of "winging it"!
Saute the fish filets in 2 tbsp butter until cooked. Remove the fish from the skillet, whisk in 1 tbsp cornstarch, then add 3/4 cup heavy cream and 3/4 cup milk to make white sauce. Return the fish to the skillet, top with diced tomato and thick slices of cheddar. Cover and simmer until the cheese melts. I served this with heart attack potatoes - so dubbed by my middle daughter when she was about 13. Sliced red skinned potatoes, boiled, with the skin on, until tender, then stirred with 1 stick of melted butter, copious amounts of freshly ground pepper, and 1/4 cup chopped parsley per 2 pounds of potatoes. Her reaction the first time I made them? "Heart attack goodness on a plate!"