The Ultimate Beef Wellington Recipe

Name: The Ultimate Beef Wellington Recipe
Prep time: 40 min
Cook time: 90 min
Total time: 130 min
Yield: 8
Ingredients: 1 center-cut beef tenderloin, trimmed of silverskin and fat, about 2 pounds (see note); Kosher salt and freshly ground black pepper; 2 tablespoons plus 1/2 teaspoon vegetable or canola oil, divided; 2 tablespoons prepared horseradish; 1 tablespoon Dijon, spicy brown, or hot English mustard; 1 pound mushrooms (button, cremini, shiitake, portabello, or a mix) cleaned, trimmed, and roughly chopped; 4 tablespoons unsalted butter; 2 medium shallots, finely diced (about 1/2 cup); 2 teaspoons finely minced fresh thyme leaves; 1/2 cup Cognac or other brandy or barrel-aged spirit, such as bourbon; 1/2 cup heavy cream; 2 teaspoons soy sauce; 4 ounces fresh foie gras (about two 1/2-inch slabs, see note); 1 sheet phyllo dough; 1/4 pound prosciutto, sliced paper thin; Flour, for dusting; 14 ounces frozen or homemade puff pastry, thawed (see note); 1 egg, beaten; Coarse sea salt, such as Maldon or fleur de sel; 1 bunch finely minced chives