2½ pounds Yukon Gold potatoes, peeled and chopped into 1-inch cubes
4 teaspoons kosher salt, divided
¾ cup unsalted butter, cubed and softened
1 clove garlic, grated
2 large egg yolks
¾ cup beef stock
2½ tablespoons Worcestershire sauce
2 tablespoons tomato paste
1 tablespoon stone-ground Dijon mustard
2 teaspoons chopped fresh rosemary
2 teaspoons chopped fresh chives
½ teaspoon ground black pepper
½ cup frozen yellow corn, thawed
½ cup frozen peas, thawed
Instructions
Preheat oven to 425°.
For filling: Heat a large Dutch oven over medium-high heat. Add half of ground beef and ½ teaspoon salt; reduce heat to medium and cook, stirring occasionally, until meat is browned and no longer pink, 3 to 4 minutes. Transfer browned beef to a large fine-mesh sieve placed over a large bowl, and let drain. Repeat with ½ teaspoon salt and remaining beef.
Return 2 tablespoons drippings to pan; discard remaining drippings. Add onion, carrot, celery, and garlic; cook over medium heat, stirring often, until onion mixture is slightly softened, 5 to 7 minutes.
Return drained beef to pan. Stir in flour; cook over medium heat, stirring often, for 1 minute. Add stock, Worcestershire, tomato paste, mustard, rosemary, chives, pepper, and remaining 1½ teaspoons salt, stirring until well combined. Bring stock mixture to a boil over medium-high heat; reduce heat to medium-low. Cook, stirring occasionally, until stock mixture is thickened and coats beef mixture, 2 to 3 minutes. Stir in corn and peas. Remove from heat; keep warm.
For topping: In a large saucepan, combine potatoes and 1½ teaspoons salt; add enough cold water to cover potatoes by 1 inch. Bring to a boil over high heat; decrease heat to medium-low and simmer until potatoes are tender, 20 to 25 minutes.
Drain potatoes; return to pan and cook over medium-low heat for 2 minutes, stirring frequently.
Add softened butter, garlic, and remaining 2½ teaspoons salt; using a potato masher, mash potatoes until butter is melted and mixture is mostly smooth (some very small chunks of potato can remain). Stir in egg yolks until combined; do not over mix. Transfer 1½ cups potato mixture into a piping bag; cut a ½-inch hole in tip.
Spoon beef mixture into a 1.5-quart baking dish placed over a rimmed baking sheet. Pipe potato mixture over top of beef mixture until completely covered; using a small offset spatula, gently smooth into an even layer all the way to edges of baking dish. Spoon remaining potato mixture into a piping bag fitted with a ½-inch open star tip*; pipe over top as desired.
Bake until potatoes are golden brown and filling is bubbly, 35 to 40 minutes. Let stand on a wire rack for 20 minutes before serving. Garnish with chives, if desired.
Notes
*We used an Ateco 827 decorating tip.
Recipe by Victoria at https://victoriamag.com/cottage-pie/