I love making vegetable gratins. You can layer flavors with different vegetables and liquids of your choosing and they meld into something magical. You can use all one type of vegetable and one type of liquid, or mix up any combination of vegetables and liquids that you like for your own unique dish.

Cooking something ‘au gratin’ is a generic term that means; baked or broiled in a shallow dish. I’m pretty sure too there is an assumption that there will be a crunchy crust on top.

I like to make this root vegetable gratin at least one or two days before I am serving it, which works out great for Holiday meals. If you make it ahead and cook it until it is ‘just done’, let it cool and then refrigerate it until the day you are serving it the gratin will have time to soak up a lot of the liquid and plump the vegetables with all that goodness.

You can make it the day you are serving it. It will be delicious but it will be more soupy than if it is left to sort itself out in a refrigerator for a day or two. The added bonus of making it ahead is that you have a beautiful dish already made that just needs to be heated up, leaving you free for other things.

Basic vegetable gratin ingredients and method.

• Olive oil
• 1 or 2 onions, leeks and or fennel sliced thin about 2 cups
• 3 pounds total root vegetables potatoes, celery root, rutabagas, carrots, turnips peeled and sliced 1/4-inch thick
• 2 1/2 – 3 cups total of any or all of cream (see note below), milk, chicken or vegetable stock. I start with 2 1/2 cups of liquid and add more when the I put everything in the casserole dish if I need more.
• 1-2 cups grated gruyere cheese (optional)
• 2 – 3 tablespoons minced fresh herbs like thyme, sage or oregano (optional)
• Salt and freshly ground black pepper
• 2 cups coarse fresh breadcrumbs or panko (optional) mixed with 2 to 3 tablespoons melted butter or oil. I didn’t use any this time, my vegetables will be crunchy on top and soft inside the casserole.

Method-Heat your oven to 375°F. Butter a deep baking dish that will hold all your vegetables. A 9 X 13 dish is usually big enough for this amount of vegetables. I used an 9 X 9 inch dish that is pretty deep. You can adjust the amount of vegetables and liquid to whatever size pan you have. This is a very forgiving method of cooking.

Heat 2 tablespoons olive oil in a large deep sauté pan over medium heat and add the onions and fennel if using. Cook until they are tender, about 10 minutes.

When the onions and fennel (if you are using it) are tender, in the largest bowl you own, combine the onion mixture with the other vegetables and 2 1/2 cups of whatever liquid you are using with about 1 scant tablespoon kosher salt and 1 1/2 teaspoons black pepper.

Mix it up really well, I use my hands. The vegetables stick together so separate them and let the liquid and cheese and onions make friends with all the root vegetables.

Pour mixture into a buttered dish and sort of organize it and smoosh it down a little. Now decide if you need more liquid. The liquid should be just below the vegetables. Add more if you need to.

If you are using breadcrumbs, mix them with butter or oil until evenly coated and distribute evenly over the top of the dish. I didn’t use breadcrumbs this time.

Bake 1 1/2 to 2 hours uncovered (I like to put any casserole on a baking tray incase anything spills over in the oven, you decide if you need to do that or not),  check the vegetables to make sure they are really tender when stabbed with a small knife and the top is browned and bubbly. Over done is better than underdone. This is just done at this point I would cook it another 1/2 hour if I was serving it right away or turn on the broiler and brown it up more. But this is fine for finishing later.

If you are serving it out of the oven let it set for 15 minutes at room temperature and serve hot. If you are making this for serving later, cover it and put it in the refrigerator.

On the day you are eating the gratin pull it out of the refrigerator at least one hour before you put it in the oven. Putting a cold ceramic or glass dish in a hot oven isn’t a good idea. Preheat the oven to 375F  and reheat it until it is brown to your liking. This picture is taken while the gratin was in the oven, the oven light makes it look yellow.

I took the picture of the gratin just out of the oven, then we all stood around and ate most of the crunchy top vegetables on top before dinner :-)

Note– Like I said, gratins are very forgiving. You can use all cream and have a very luxurious dish. I love using all cream with potatoes and celeriac. It makes a gorgeous holiday side dish . You can use all stock and have a light dish highlighting all the vegetables. Today I used a little cream, like 1/2 cup and the rest milk. If I needed more liquid I was going to make some vegetable stock from the bouillon base and top it off. I didn’t need it though and to be honest; I wanted to use up the milk to make room in the refrigerator for other stuff otherwise I probably would have used some stock.