Mac and I love scalloped or au gratin potatoes – almost any potato casserole, actually. I have several different recipes that I make now and then, some with ham and other vegetables, and most with just potatoes, onions and cheese. I found a new one not long ago and decided to prepare it the day before yesterday. It called for celery root (celeriac) and parsnips, not ingredients that I usually have on hand. After a trip to a large grocery that I was sure would carry them, we came home ready to experiment.
The two other root vegetables add a subtle taste to the more bland potatoes. While parsnips, especially old ones, can be bitter, they add a slightly nutty taste to the casserole.
Celery root has a slight celery taste, but it is hard to describe adequately. It can be eaten raw, or cooked.
This recipe is from Cook’s Illustrated magazine’s website and, I believe, is a variation of a recipe for scalloped potatoes printed in an earlier issue. While the authors recommend using a food processor to quickly and evenly slice the vegetables to 1/8″, I had no difficulty using a santoku knife for all the slicing. It would have taken more time to get my processor, set it up, and then clean it. I rarely use it for slicing ingredients for ordinary recipes. If I were to make enough for a large group, I would probably use the processor.
SCALLOPED POTATOES WITH ROOT VEGETABLES
2 T. unsalted butter
1 medium onion, minced (about 1 cup)
2 medium cloves garlic, minced or pressed (about 2 teaspoons)
1 T. chopped fresh thyme leaves
1 1/4 t. table salt
1/4 t. ground black pepper
8 ounces celery root (about 1/2 medium), peeled and sliced 1/8 inch thick
8 ounces parsnips (about 2 medium), peeled and sliced 1/8 inch thick
1 c. low-sodium chicken broth
1 c. heavy cream
2 bay leaves
1 1/2 pounds russet potatoes (about 2 large), peeled and sliced 1/8 inch thick
4 ounces grated cheddar cheese, shredded (about 1 cup)
1. Adjust oven rack to middle position; heat oven to 425 degrees.
2. Melt butter in large Dutch oven over medium-heat until foaming subsides. Add onion and cook, stirring occasionaly, until soft and lightly browned, about 4 minutes. Add garlic, thyme, salt and pepper; cook until fragrant, about 30 seconds. Add celery root, parsnips, chicken broth, cream, and bay leaves and bring to simmer. Cover, reduce heat to medium-low, and simmer for 5 minutes. Add potatoes, bring mixture back to simmer, cover, and cook until potatoes are almost tender (paring knife can be slipped into and out of potato slice with some resistance), about 10 minutes. Discard bay leaves.
3. Transfer mixture to 8-inch square baking dish (or other 1 1/2-quart gratin dish) and press into an even layer; sprinkle evenly with cheese. Bake until cream is bubbling around edges and top is golden brown, about 15 minutes. Cool 10 minutes before serving.
4. To make ahead: Once the scalloped vegetables have been transferred to the baking dish and pressed into an even layer in step 3, they can be wrapped in plastic wrap and refrigerated for up to 24 hours. When ready to bake, add the cheese, cover with foil, and bake in a 400-degree oven until the mixture is hot and bubbling, about 45 minutes. Remove the foil and cook until the cheddar begins to brown, about 30 minutes longer. Let cool for 10 minutes before serving.
(Parmesan cheese can be used instead of cheddar. As a matter of fact, other cheeses, gruyere for example, are also possibilities.)