It seems so sad to see some of the garden vegetables no larger baring and being plowed under to await another year. We do have fall crops to be grateful for, potatoes, turnips, cabbage, etc.
My mom made something very much like this, but I doubt she called it a "gratin". If it had turnips in it, I was there. Never met a turnip I didn't love. It's hard to believe that people once viewed turnips as "poor-people's food".
4 firm waxy potatoes, such as red-skinned (about 1 pound)
4 medium white turnips (about 1 pound)
1 1/4 cups heavy cream
Salt and freshly ground black pepper
A pinch of freshly grated nutmeg
2-3 ounces Swiss Gruyere cheese, grated
3 tablespoons butter, cut in pieces
Wash, but do not peel, the potatoes and put them into a pan of cold salted water, bring to the boil and cook for 20 minutes. You can also steam them.
Peel the turnips and cook in the same manner, but for 15 minutes; they should be tender but still somewhat firm.
Preheat the oven to 35o degrees F.
Cool the potatoes and turnips in cold water until you are able to handle them. Peel the potatoes and cut both the potatoes and the turnips into 1/8-inch slices.
Pour the cream into a deep skillet or wide casserole; season with salt, pepper, and nutmeg, and bring slowly to the boil. Add the potatoes and turnips and mix carefully to avoid breaking the slices.
Turn the mixture into a buttered gratin dish or baking dish. Sprinkle with grated cheese and dot with butter. Bake for 20-30 minutes. If the top is not browned by this time, raise the oven heat to 475 degrees, or run under the broiler for a moment.