Snowcap Summit Cottage Pie

Procedure

1. Start the snow. Put the Yukon Gold potatoes in a large pot, cover with cold water by 1 inch (2.5 cm) and add 1 tablespoon kosher salt. Bring to a boil, then simmer until a knife slides in with no resistance, 15 to 18 minutes. Starting in cold water cooks them evenly to the center.⏱ 18:00
2. Brown the beef. Meanwhile, heat the olive oil in a 12-inch (30 cm) oven-safe skillet over medium-high heat. Press the ground beef into an even layer, sprinkle with ½ teaspoon of the kosher salt and sear, undisturbed, until a deep brown crust forms, about 4 minutes. Break it up and cook until no pink remains and it reaches 160°F (71°C), 3 to 4 minutes more. Spoon off all but 2 tablespoons of the fat.⏱ 4:00⏱ 4:00
3. Build the base. Add the yellow onion, carrots, celery and the remaining 1 teaspoon kosher salt and cook, stirring, until soft, 6 to 8 minutes. Stir in the garlic and tomato paste and cook until the paste darkens to brick red, about 2 minutes. Sprinkle in the all-purpose flour and stir 1 minute.⏱ 8:00⏱ 2:00
4. Simmer the gravy. Pour in the beef broth and Worcestershire sauce, scraping up the browned bits. Add the thyme leaves and black pepper and simmer until the gravy coats a spoon, 8 to 10 minutes. Take the skillet off the heat and stir in the frozen peas; they stay bright and sweet. Heat the oven to 400°F (200°C).⏱ 10:00
5. Mash. Drain the potatoes and return them to the hot pot for 1 minute to steam dry. Mash with the butter until smooth, then beat in the warm milk and white pepper and season with kosher salt to taste. Cool 5 minutes, then beat in the egg yolk.⏱ 1:00⏱ 5:00
6. Pipe the peaks. Spoon the mash into a piping bag fitted with a large star tip, or into a zip-top bag with a corner snipped off. Pipe tall peaks over the filling, edge to edge, so no gravy shows. No bag? Spread the mash and pull it up into points with a fork.
7. Bake and gild. Set the skillet on a foil-lined sheet pan and bake until the gravy bubbles at the edges, about 20 minutes. Switch the oven to broil and broil, watching closely, until the tips turn golden, 2 to 4 minutes.⏱ 20:00⏱ 4:00
8. Claim the summit. Rest the pie 10 minutes so the gravy sets. Plant the thyme sprig on the tallest peak and serve.⏱ 10:00