2 cups applewood chips (NOT soaked); a stovetop smoker or 6-inch hotel pan and a 4-inch perforated hotel pan
Whisk together the curry paste, soy sauce and juice of 3 limes in a small bowl. Add 3 ounces olive oil and whisk to combine.
Sprinkle the salmon with salt and pepper, then pour the curry marinade over the top, coating the fish completely.
Meanwhile, peel and dice half the celery root. Add to a pot and cover with the milk. Bring to a simmer and season with salt. Cook until tender, about 15 minutes, then drain, discarding the milk. Add the celery root to a blender along with the butter and puree until smooth. Pour back into the pot and keep warm.
Julienne the other half of the celery root and add to a mixing bowl. Add the apples and the juice of the remaining 3 limes. Drizzle with olive oil and season with salt and pepper, then fold in the cilantro leaves. Set aside.
Preheat the oven to 250 degrees F.
Set up a smoker by adding the wood chips to the bottom of a stovetop smoker or 6-inch hotel pan. Place the perforated smoker insert or a 4-inch perforated hotel pan inside. Add the salmon to the perforated pan and cover tightly with foil. Place the pan on top of two stovetop burners and heat until the chips start smoking. Transfer the pan to the oven and cook until the salmon reaches an internal temperature of 135 to 140 degrees F, 30 to 40 minutes.
To serve: Spoon the celery root puree onto a plate. Top with a piece of salmon, followed by the celery root salad on top. Repeat to make 3 more servings.