• 1 pound Yukon Gold potatoes, scrubbed
• 3 large egg yolks, room temperature
• 1 large egg, room temperature
• 1/2 cup sour cream, room temperature
• 1/4 cup all-purpose flour
• 1 1/2 teaspoon kosher salt
• 1/2 teaspoon finely ground black pepper
• 1/4 teaspoon baking soda
• 1/4 teaspoon ground nutmeg
• 2 tablespoons unsalted butter, melted, slightly cooled
• A food mill or potato ricer