Makes 8 servings
1 homemade tart shell or refrigerated pie crust (blind baked)
1 large head cauliflower, cut into florets
1 large yellow onion, cut in half and thinly sliced
1 8 -ounce package Mascarpone cheese (substitute sour cream for a lighter version)
1 cup grated Gruyere (or substitute Swiss OR fontina/Parmesan combo)
2 tablespoons grated Parmesan
1/2 cup heavy cream
2 large eggs
Truffle oil (optional)
Pinch of ground nutmeg
Salt and Pepper
Step 1: Preheat the oven to 425 degrees F. Toss the cauliflower with a generous amount of olive oil to coat, as well as salt and pepper to taste. Place the cauliflower on a baking sheet and roast for about 20 minutes, making sure to flip once or twice along the way. The florets should just be getting golden. Remove the florets from the oven and set aside. Lower the temperature to 350 degrees F.
Step 2: While the florets are roasting, youíll caramelize the onion. Cut the onion in half and thinly slice it, then add about a tablespoon of olive oil to a large pan over medium-high heat. Add the sliced onion as well as a dash of salt and pepper to the pan.
Step 3: Cook the onion for about seven minutes, stirring occasionally, until it gets tender and translucent — then reduce the heat to low. (Add a pinch of sugar once you reduce the heat for a little sweetness.) Then, let the onion slices cook on low until they become a deep golden or brown color– it takes about 20 minutes for them to caramelize. Stir them often enough so they don’t burn the bottom of the pan, but make sure they have enough time to sit in the oil and caramelize. Add a little water to the pan if they start to stick too much to the bottom.
Step 4: Once the cauliflower is cool, thinly slice the florets so they are about 1/4-inch thick. Toss with a drizzle of truffle oil (if desired) and set aside.
Step 5: Mix together the eggs, mascarpone, cream, nutmeg, and salt and pepper to taste. Then, add the Gruyere (or substitute) to the mixture.
Step 6: Press your crust into a 9-inch tart pan, trimming any excess from the edges with a knife. If the crust didn’t come refrigerated, you will want to refrigerate it for 30 minutes after pressing into the pan and before assembling the tart.
Step 7: Place the pastry shell on a rimmed baking sheet (to catch any drips) and coat the bottom of the pastry shell with Dijon mustard (the mustard layer should only be 1/8-inch thick). Then, spread the onions evenly over the bottom of the pastry shell, followed by the roasted cauliflower.
Step 8: Pour the cheese and cream mixture over the onions and cauliflower, and then top the tart with the grated Parmesan cheese. Place the baking sheet into the oven and bake for about 40 minutes and you wíll want the top to be golden brown and the center to be set.
Step 9: Let the tart cool for about 15 minutes before serving.