Preheat the oven to 350 degrees F.
Grease a baking sheet with the oil. Season both sides of the salmon fillets with 1/4 teaspoon salt and 1/2 teaspoon pepper and place on the baking sheet. Roast until the center is still slightly pink, about 10 minutes. Remove from the oven.
Meanwhile, to make the Granny Smith apple butter sauce, in a medium saucepan, combine the diced apples, sugar, and hard cider. Cook over medium-high heat until the apples are translucent, about 5 minutes. Add the cream and cook until reduced by half, about 3 minutes. Add the butter several pieces at a time, whisking constantly to blend, and removing from the heat periodically to prevent the sauce from breaking. Add the remaining 1/4 teaspoon salt and 1/8 teaspoon white pepper and whisk to blend. Remove from the heat and cover to keep warm until ready to serve, stirring occasionally.
Place 1 potato cake on each plate and top with a salmon fillet. Drizzle each portion with the apple butter. Top with 1/4 of the salmon and garnish with 1 teaspoon of the caviar. Serve immediately.
Yield: 4 servings