This section is from the book "Economical Cookery", by Marion Harris Neil. Also available from Amazon: Economical Cookery (1918).
1 tablespoon (1/2 oz.) butter substitute 1 tablespoon flour
2 cups (1 pt.) milk
1/2 teaspoon salt
1/4 teaspoon pepper
1/2 cup (2 ozs.) grated cheese reel potatoes, cut into dice and boil until tender m boiling salted water, and drain. Blend butter and flour in a saucepan over the fire, add milk and seasonings, and bring to boiling point and cook two minutes. Place potatoes in greased fireproof dish, pour over sauce, sprinkle over with cheese, dot with tiny pieces of butter substitute, and brown in oven. Serve hot.
The word gratin comes from the verb gratiner - to make brown - and implies a shallow dish, so that the whole contents shall be exposed to baking. All vegetables served au gratin should first be boiled, then placed in a shallow dish, covered with fine bread crumbs and butter, or with a sauce, and then baked in a hot oven until brown. Cauliflowers, carrots, parsnips, artichokes, salsify, and celery all lend themselves well to treatment au gratin. Tomatoes sliced, laid in a gratin dish, covered with a layer of bread crumbs, chopped herbs, and seasonings, with pats of butter on top, also make one of the very nicest of gratins.