Onion Au Gratin
Peel and slice thinly three good-sized Spanish onions; Butter a baking dish, arrange in it a layer of the sliced onions, dust with salt and pepper, sprinkle over one tablespoonful of bread crumbs and one tablespoonful of melted butter. Continue in this order until the pan is filled. Bake in a moderate oven until the onions are tender; this will take about three-quarters of an hour. Over the top sprinkle a thick layer of grated cheese and return to the oven until it is melted and browned.
A plain layered onion gratin with no liquid and no sauce — the onions supply their own moisture, which is the whole trick. A few things want translating.
- Moderate ovenSet it at 350F. The final browning of the cheese goes faster under a broiler if the top is still pale after the onions are done.
- Spanish onionsThe large, mild, straw-skinned sort, roughly 3/4 to 1 lb each. Three of them sliced make a considerable quantity; the recipe simply says to build up layers until the pan is filled, so choose the dish to suit. Ordinary yellow onions work but are sharper and give a more assertive dish.
- Slice thin and mean itAn eighth of an inch or less, ideally on a mandoline. Thick slices will not be tender in 45 minutes and the layers stay crunchy in the middle while the top browns.
- Cover for the first halfWith no stock or cream, the dish depends on steam from the onions themselves. Foil or a lid for the first 25 minutes, then uncovered, gives you tender onions without a dried-out top layer.
- CrumbsPeriod recipes of this kind usually meant dry, sieved crumbs from stale bread, closer to fine dry crumbs than to panko, though soft fresh crumbs were also in use. Fresh soft crumbs will work but soak up butter and go soggy between the layers.
- Butter quantityOne tablespoon of crumbs and one of melted butter per layer means three or four of each for a full dish, so about 1/4 cup butter total. Brush rather than pour so it does not pool at the bottom.
- Cheese"Grated cheese" in an American book of this period would most often have been a firm aged Cheddar or a dry "store cheese." Four to six ounces is a thick layer. Parmesan browns well but gives a drier crust.
- YieldServes four to six as a side. It benefits from ten minutes' rest out of the oven — straight from the heat the layers slide apart.
Onions cooked au gratin — with crumbs, butter and browned cheese — belong to the late nineteenth-century American appetite for French-sounding vegetable dishes that could be assembled from a plain pantry. Large sweet onions were sold as "Spanish" onions in the period whether or not they came from Spain, the name marking the mild, thick-fleshed type against the small sharp cooking onion. Note that the recipe assumes no sauce at all, trusting butter, crumbs and cheese to do the work.