2 lbs. Red Dog Farm Celeriac, peeled and cut into 1/2-to-3/4-inch cubes
2 cups vegetable broth, or more if necessary
1 teaspoon sea salt
1/4 cup olive oil or butter
1 large Onion, sliced thinly
1 clove Garlic, minced
1 1/2 tsp thyme
2 Tbsp white wine or dry cider
1 bunch Red Dog Farm Lacinato Kale, rinsed (but not dried) and torn into pieces
1/8 tsp black pepper
3 ounces white or whole-wheat bread
1/3 cup walnut halves or pieces
Place the celeriac pieces in a large saucepan; add enough of the broth to barely cover, reserving at least 1/4 cup of the broth from the original 2 cups. Cook over medium heat; once the liquid starts to bubble, cook for about 5 minutes or until the celeriac is fork-tender. Turn off the heat.
Heat half of the oil in a heavy saute pan or Dutch oven over medium heat. Once the oil shimmers, add the onion and 1/4 teaspoon of the salt, stirring to coat. Reduce the heat to medium-low; cook for 5 minutes or until the onion is translucent, then stir in the garlic and thyme. Cook for 5 to 7 minutes, until the onion is tender and starting to pick up color.
Stir in the wine or cider; cook for a minute or two.
Use a slotted spoon to transfer the celery root to the onion mixture, stirring gently to incorporate. Season with 1/4 teaspoon of the salt, and cook for a few minutes (over medium-low heat) to meld the flavors. Transfer the mixture to a mixing bowl. Discard the remaining broth used to cook the celery root, or reserve for another use.
Pour 1 tablespoon of the oil into the same saute pan or Dutch oven over medium heat; once the oil shimmers, add the kale and half of the reserved broth. Season with 1/4 teaspoon of the salt, stirring to coat. Reduce the heat to medium-low; partially cover and cook for 3 to 10 minutes until softened, depending on the toughness/type of the kale used. Stir occasionally; reduce the heat to low if the kale seems dry, or add the remaining reserved broth.
Transfer to the mixing bowl and season with the pepper and remaining salt. Preheat the oven to 375 degrees. Have a shallow 2-quart baking dish at hand.
Tear the bread into chunks, dropping them into a food processor as you work. Pulse to form coarse bread crumbs, then transfer to a separate bowl. Pulse the walnuts in the food processor briefly, just until coarsely chopped, then add to the bread crumbs. Drizzle the mix with the remaining 1 tablespoon of oil and toss gently to coat.
Spread the celery root-kale mixture in the baking dish. Sprinkle evenly with bread-crumb-walnut mixture. Bake for about 25 minutes or until the top is deep golden and the gratin is bubbling.
Wait for 10 minutes before serving.