Portobello and Celery Root Shepherd’s Pie

Preheat the oven to 400°F. Rinse and dry all produce. Dice the carrots, turnips, onions, celery root, and potatoes. Mince the garlic and chop the thyme. Dice the portobello stems and one of the caps to match the size of the diced carrots and turnips. Set aside.

Using a pastry brush (and if you don't have one, you can use the edge of a napkin), apply 2 tablespoons of olive oil to the remaining four portobello caps. Place them on a sheet pan, rounded sides up, and sprinkle with ½ teaspoon of salt.

Roast the caps for 8 to 12 minutes, or until they have lost some of their water volume—you will see liquid build up outside the mushroom shell. Remove from the oven and set aside.

Toss the diced portobellos, carrots, turnips, onions, and garlic with 2 tablespoons olive oil, ½ teaspoon of salt, and ½ teaspoon of pepper. Spread the mixture on a sheet pan and roast until the carrots and turnips are fork-tender, 12 to 15 minutes. Remove the roasted vegetables from the oven and toss in the mustard and thyme. Set aside.

Bring a medium pot of salted water to a boil over high heat. Add the celery root and potatoes and boil until fork-tender, 8 to 12 minutes. Then, drain the celery root and potato, reserving ¼ cup of the cooking water. Transfer the celery root, potato, and reserved cooking water to a food processor or blender, add the truffle oil, and ½ teaspoon salt and ½ teaspoon pepper. Pulse until smooth and creamy.

Turn the remaining portobello caps upside down and stuff them with the roasted diced vegetables. Seal the caps by completely covering the diced vegetables with the celery root and potato puree. Return the caps to the oven and bake until the puree on top starts to brown, 6 to 10 minutes. Serve immediately.