1 1/2 pounds russet potatoes 3/4 teaspoon kosher salt 1/4 teaspoon freshly ground black pepper 1 egg yolk 2 tablespoons vegetable oil 1 cup chopped onion 2 carrots, peeled and diced small 2 cloves garlic, minced 1 1/2 pounds ground beef, turkey or chicken 1 teaspoon kosher salt 1/2 teaspoon freshly ground black pepper 2 tablespoons all-purpose flour 2 teaspoons tomato paste 1 cup chicken broth 3 teaspoons fresh herbs such rosemary or thyme or 1 teaspoon dry herbs 1 cup frozen vegetables (optional) Peel the potatoes and cut into large chunks. Place in a medium saucepan and cover with cold water. Set over high heat, cover and bring to a boil. Once boiling, uncover, decrease the heat and cook until tender. Drain the potatoes in a colander and then return to the saucepan. Mash the potatoes and then add the salt and pepper and continue to mash until smooth. Stir in the yolk until well combined.
Preheat the oven to 400 degrees F. Pour the oil into a 12-inch saute pan and set over medium high heat. Add the onion and carrots and saute for 3 to 4 minutes. Add the garlic and stir to combine. Add the meat, salt and pepper and cook until browned and cooked through, approximately 3 minutes. Sprinkle the meat with the flour and toss to coat, continuing to cook for another minute. Add the tomato paste, chicken broth, herbs, and stir to combine. Bring to a boil, reduce the heat to low, cover and simmer slowly 15 minutes or until the sauce is thickened slightly. Add the frozen veggies to the meat mixture and spread evenly into an 11 by 7-inch glass baking dish. Top with the mashed potatoes, starting around the edges to create a seal to prevent the mixture from bubbling up and smooth with a rubber spatula. Bake for 25 minutes or just until the potatoes begin to brown. Remove to a cooling rack for at least 15 minutes before serving