1. Peel the potatoes but do not wash them; their starch enables them to stick together. Trim the celery root of all brown spots; set a small piece of it aside. Use the julienne blade of a mandoline or food processor to make a fine julienne of both the potatoes and celery root and mix them together.

2. Place about 1 tablespoon olive oil in a 10-inch nonstick skillet and tum the heat to medium-high. When it is hot (a piece of the potato mixture will sizzle), scatter about ¼ cup of the potato-celery root mixture loosely over the surface of the oil; the object is to make a lacy doily of the mixture. It’s not difficult; the key is to not put too much of the mixture in the pan; you can always add a few more strands. Just make certain you do not completely cover the bottom of the pan. Cook, encouraging the outer strands to stick to those in the middle by prodding with a spatula, until lightly browned on one side; do not let the pancake become too crisp. Turn and cook the other side, then drain on paper towels and sprinkle with salt. Repeat, adding more oil as necessary (they don’t absorb much, so don’t overdo it). lt’s easiest to have two skillets going at once, and feel free to make these several hours in advance; just reheat the crisps in the oven as you cook the salmon.

3. Using the finest grater you have, grate enough of the reserved small piece of celery root to make 1 tablespoon. Grate enough of the celery to make 1 tablespoon. Grate enough of the horseradish to make 1 tablespoon. Set aside for a moment.

4. Lightly beat the cream; it should be soft and thick, but not hold even a soft peak. Stir in the grated vegetables, then season with cayenne and salt to taste. Stir in 2 teaspoons of the lemon juice and 2 tablespoons of the chives.

5. Use a carving or slicing knife to cut the salmon on a 20° to 30° angle into twelve 1/2-inch-thick slices. Place them in a shallow roasting pan and sprinkle them with salt, cayenne, and 1/4 cup each of the remaining olive oil and lemon juice. Let sit while you preheat the oven to 400°F; turn over once after about 5 minutes.

6. Place the salmon and its marinade in the oven. Roast for about 2 minutes, then turn over; roast for another 2 minutes or so, until the salmon is pale on the outside but still a little rosy within.

7. Place a piece of salmon on each of 4 plates, then cover it with a potato pancake. Repeat, making 3 layers on each plate. Garnish with minced chives and serve with the celery-horseradish cream.