Sweet Potato and Fennel Gratin with Caramelized Onions

Loaded with fiber and flavor, this hearty, creamy, cheesy vegetable dish uses the best flavors of the season. It's an excellent accompaniment to beef and makes a satisfying vegetarian main. You can assemble the gratin up to half a day in advance and bake when ready to serve. This recipe makes 8 servings.

PREP TIME: 15 minutes
COOK TIME: 1 hours 0 minutes

Ingredients
For the caramelized onions:
1 large yellow onion, chopped
1 tablespoon butter
1 tablespoon olive oil
Salt, to taste

Remaining ingredients:
2 pounds sweet potatoes, peeled and sliced into 1/8" rounds
1 large fennel bulb, root end removed and thinly sliced
2-3 cloves garlic, minced or grated
1 1/4 cups heavy cream, divided
3/4 cup shredded parmesan
1/2 cup shredded gruyere
Leaves from 1 spring fresh thyme
1/8 teaspoon ground nutmeg
1/2 teaspoon salt

Directions
Make the caramelized onions: Heat butter and oil in a large, heavy skillet to medium heat on the stove top. Add onions and stir to coat all of the onions with the fat. Cook, stirring every few minutes, until the onions turn a golden caramel color; the entire process should take about 25-30 minutes. Season lightly with salt the last few minutes of cooking. Once the onions are caramelized, remove from heat and let cool for a few minutes.

Preheat your oven to 375 F.

Add sweet potatoes and fennel and to a large mixing bowl. Pour 1/4 cup cream over the vegetables and season with the salt. Toss gently with your (clean) hands to coat all of the vegetables with the cream.

Toss the parmesan and gruyere together in another bowl.

In another bowl, combine the garlic, remaining cup of cream, thyme leaves and nutmeg.

Spray a large glass baking dish with nonstick cooking spray. Add a layer of sweet potatoes, then fennel, a scoop of the onions and a handful of the cheese mixture. Repeat this process until all of the vegetables and cheese are used. Pour the garlic and cream mixture over the vegetables and cheese in an even layer.

Cover tightly with foil and bake for 45 minutes. Test the vegetables by piercing the center of the gratin with a sharp knife; the vegetables should be tender. If the vegetables are still hard, put the foil back onto the dish and bake for another ten minutes. Once the veggies are tender, remove the foil and bake for another 10 minutes to brown the top.

Remove from oven and let stand for a few minutes before serving.