Preheat the oven to 350 degrees F. Line a baking sheet with foil.
For the mashed potatoes: Poke each potato with a fork several times and microwave until soft, about 15 minutes (or use your microwave?s potato setting). Cool until you are able to handle them with a towel, about 2 minutes. Halve the potatoes and scoop out the flesh with a spoon and discard the skin. Mash the potatoes and butter in a medium bowl until smooth then fold in the sour cream, chives and 1 teaspoon salt until well combined. Set aside.
For the meatloaf: Toast the bread crumbs in a dry skillet over medium heat until browned and fragrant, about 1 minute. Transfer to a large mixing bowl and set aside. Add the oil, onions, garlic, oregano, 1/2 teaspoon salt and 1/2 teaspoon pepper to the skillet and cook, stirring, until onions are tender, about 8 minutes. Let cool slightly. Add the onion mixture to the bread crumbs along with the meatloaf mix, Parmesan and Worcestershire sauce. Toss and mix gently. Add the eggs and mix it completely into the meat mixture.
Transfer 1/2 of the meatloaf mixture to the prepared baking sheet and gently press into a 12- by-3-inch rectangle. Gently create a well down the middle of the meatloaf mixture with a 1/2-inch wall on all four sides. Spoon the mashed potato mixture into the well. Working with a quarter of the remaining meatloaf mixture, gently flatten the mixture with the palms of your hands. Lay the meatloaf mixture over 1/2 of the mashed potatoes. Repeat with the remaining meatloaf mixture ensuring the potatoes are completely enclosed.
For the glaze: Whisk together the ketchup, brown sugar and vinegar in a small bowl. Spoon the glaze evenly over the entire loaf.
Bake until an instant read thermometer registers 160 degrees F in the center of the loaf, about 45 minutes.
While the meatloaf is cooking, cook the peas according to package directions. Toss with the butter and season with salt and pepper. Keep warm.
Slice and serve the meatloaf with butter, black pepper and the peas.
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