Serves 6 to 8

1 pound medium beets

3 sprigs fresh thyme branches plus 3/4 teaspoon fresh thyme leaves

2 garlic cloves, peeled

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¼teaspoon black peppercorns

Kosher salt and ground black pepper

1 ¼ pounds beet greens, Swiss chard or a mix of both

11 tablespoons cold unsalted butter, more for greasing pan

3 cups all-purpose flour

2 cups milk

9 ounces sharp cheddar, preferably clothbound, grated (2¼ cups)

2 to 3 tablespoons English mustard powder, to taste

1 teaspoon Worcestershire sauce

½ teaspoon Tabasco sauce, more as needed

¼ cup rolled oats

3 Tablespoons toasted hazelnuts, chopped

1½ teaspoons grated Parmigiano-Reggiano

¼ teaspoon freshly grated nutmeg

1. Combine beets, thyme branches, garlic and peppercorns in a large pot. Cover with cold salted water. Bring to a simmer over medium-high heat; cook until beets are tender, 15 to 30 minutes depending on size. Remove with a slotted spoon. Add greens and cook for two minutes (do this in batches if necessary); remove with tongs and transfer immediately to a bowl of ice water. Drain well.

2. Once beets are cool enough to handle, peel them and slice crosswise into ¼-inch-thick slices. Roughly chop greens’ leaves and stalks.

3. Prepare the béchamel: In a small saucepan over low heat, melt 5 tablespoons butter. Stir in 2
3 cup flour. Cook, stirring constantly, for two minutes; roux should smell cooked but remain white. Slowly whisk in milk until mixture forms a thick, smooth sauce. Stir in 8 ounces of cheddar (2 cups) until melted. Stir in mustard powder, Worcestershire and Tabasco. Season with salt to taste.

4. Make the crumble topping: In a small bowl, stir together remaining 2
3 cup flour, the oats and the hazelnuts. Use your fingers to work in 6 tablespoons butter, the remaining 1 ounce cheddar (¼ cup) and the Parmigiano-Reggiano. It should be a mixture of large and small pieces. Season with a pinch of salt, pepper and the nutmeg.

5. When you are ready to assemble the dish, heat oven to 350 degrees. Butter a 2-quart gratin or baking dish. Spread a layer of béchamel on the bottom. Top with a layer of beets, followed by a layer of greens and stalks. Season generously with salt and pepper, and sprinkle with thyme leaves. Spread another layer of béchamel on top and repeat process to fill dish (you will end up with three or four layers). Cover entire surface with crumble topping. Transfer dish to oven and bake until bubbling and golden brown in spots, 45 minutes to 1 hour.

— Adapted by Melissa Clark, The New York Times, from Nicholas Wilber, the Fat Radish, New York