Scallion Potato Pancakes with Vinegar Cream

Name: Scallion Potato Pancakes with Vinegar Cream
Ingredients: Scallion Potato Pancakes; 1 russet potato, large; 1/2 cup scallions, green and white parts only, thinly sliced; 1 tablespoon butter, melted; 1 pinch salt; 1 pinch white pepper; 3 tablespoons duck fat; Vinegar Cream; 1/2 cup heavy cream; 1 teaspoon red wine vinegar; 1 scallion, dark green part only, finely chopped; 1/2 teaspoon garlic, finely grated; 1 teaspoon tarragon leaves, finely chopped; 1 pinch freshly ground black pepper