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Celery Root and Squash Gratin with Walnut-Thyme Streusel Recipe
(recipe, Michelle D ~ aka Sage)
In this gratin, layers of celery root and squash are bathed in cream and topped with crunchy walnut- and thyme-studded breadcrumbs, making for a crowd-pleasing side.
You can make this up to 1 day ahead and rewarm it, covered, at 350°F for about 20 to 30 minutes before serving.
- 1 cup panko
- 4 Tbsp. unsalted butter (½ stick), melted
- ½ cup finely chopped walnuts
- 1 Tbsp. finely chopped fresh Italian parsley
- 1½ tsp. fresh thyme leaves
- 1 tsp. kosher salt
- 1¼ cups heavy cream
- 1 medium butternut squash (about 3 pounds), peeled, cut in half, and seeded
- 1 medium celery root, also known as celeriac (about 1 pound), peeled and cut in half
- 2 Tbsp. unsalted butter
- ½ medium white onion, thinly sliced
- For the streusel:
- Combine all ingredients in a medium bowl and mix until butter is incorporated. Cover and place in the refrigerator until ready to use.
- For the gratin:
- Heat the oven to 400°F and arrange a rack in the middle. Coat a 13-by-9-inch baking dish with butter and set aside.
- Pour cream into a large bowl and set aside. Slice squash and celery root into ¼-inch-thick pieces with a mandoline or sharp knife, placing pieces into the cream as they are cut. Toss until well coated.
- Melt butter in a medium frying pan over medium heat. When it foams, add onion and season well with salt and freshly ground black pepper. Sauté until soft and translucent, about 5 minutes; set aside.
- Construct gratin by ladling ⅓ of the squash and celery root mixture into the baking dish, then seasoning well with salt and freshly ground black pepper. Top with ½ of the onions, then another layer of squash and celery root. Season the second layer with salt and pepper and cover with the remaining onions. Place the last of the squash and celery root on top and press down to create an even surface. Season with salt and pepper, then pour the remaining cream over top.
- Sprinkle streusel evenly over gratin. Bake until vegetables are soft and streusel is golden brown, about 40 to 50 minutes. Let sit at room temperature for about 20 minutes before serving.