Pour the water and white wine in a large skillet and bring to a boil. Turn off heat.
Place the salmon fillets in the skillet; let stand for 6 minutes. Turn salmon over; let stand for 5 minutes.
Bring the liquid just to a simmer and cook until the salmon is just cooked through, about 30 seconds. Using a slotted spatula, transfer the salmon to a plate and cool.
Place the potatoes in a pot of cold salted water. Bring to a boil. Cook until tender, about 15 minutes. Drain. Allow to cool and cut into quarters.
In a medium bowl, whisk 10 Tablespoons of the cream, 4 Tablespoons of the horseradish and 3 Tablespoons of the dill, until stiff peaks form.** Whisk in the vinegar. Season with salt and pepper to taste. Cover and refrigerate.
With a fork, flake the cooked salmon into bite-sized pieces.
In a medium bowl, mash 1 1/2 cups of the cooked/cooled potatoes with the remaining 4 Tablespoon of cream, the remaining 2 Tablespoons of horseradish and the remaining 1 Tablespoon of dill until almost smooth.
Gently fold in both salmons (cooked and smoked), the scallions and the remaining potatoes. Season with salt and pepper.
Everything can be covered and refrigerated at this point and stored in the refrigerator for up to one day ahead. Remove the potato/salmon mixture from the refrigerator 30 minutes prior to continuing.
In a large nonstick skillet, melt the butter over high heat. Add the hash and press to compact. Reduce the heat to medium and cook until the bottom is brown and crusty, about 10 minutes.
Using a large spatula, turn the hash over in sections, (or use the technique found on the Tortilla Española post).
Press lightly to compact and shape the mixture until the bottom is browned, about 5 minutes.
Turn the hash out onto a serving plate. Serve with the Horseradish Dill Sauce.