Lamb Shepherd's Pie with Puff Pastry

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  2 lbs Ground Lamb
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  2 Yellow Onion(220g)
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  2 Carrots(122g)
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  4 Garlic(12g)
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  3 tbsp Thyme, Fresh
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  2.5 cup Low Sodium Beef Broth
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  12 oz Beer, Stout
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  1 tsp 1 teaspoon sea salt
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  0.5 tsp ½ teaspoon freshly cracked black pepper
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  3 tbsp Cornstarch
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  1 cup Peas, Sweet, Frozen
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  2 Puff Pastry Dough, Frozen, Thawed(500g)
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  1 Egg, Whole, Large(44g)
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  1 cup Cheese, Gruyere
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  4 Potato, Russet, Baked, Flesh Only(624g)
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  1 tsp 1 teaspoon sea salt
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  0.3 cup Cream, Heavy Whipping
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  4 tbsp Unsalted Butter
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  0.5 tsp ½ teaspoons freshly cracked black pepper

Instructions

1. 1Preheat the oven to 350°F with a rack in the center position. Grease 8 (4-inch) disposable pie tins or oven-proof cocottes.
2. 2In a large skillet over medium-high heat, cook the ground lamb, breaking it up with a spoon, until browned (8–10 minutes). Transfer to a plate with a slotted spoon, leaving 2 tablespoons of fat in the pan. Add the onion and carrots, cook over medium heat until the onion is translucent (about 5 minutes). Stir in the garlic and fresh thyme, cook until fragrant (about 1 minute). Return the lamb to the pan, add the beef broth and stout beer, stir to combine, cover with a lid, and transfer to the oven for 1 hour.
3. 3While the lamb braises, bring a large pot of salted water to a boil over high heat. Add the russet potatoes and cook until just fork-tender (about 15 minutes). Drain and set aside.
4. 4Remove the lamb mixture from the oven. In a small bowl, whisk the cornstarch with 4 tablespoons of cold water until dissolved. Stir the cornstarch slurry into the lamb mixture, then stir in the frozen peas. Return to the oven until the sauce thickens (about 30 minutes). Remove and let cool completely before filling the pies.
5. 5In the pot used for the potatoes, combine the heavy cream and butter over medium heat, stirring until the butter melts (about 2 minutes). Using a potato ricer, rice the cooked potatoes over the hot butter mixture. Season with sea salt and cracked black pepper to taste.
6. 6Increase the oven temperature to 400°F. On a lightly floured surface, roll the puff pastry dough to ⅛ inch thick and cut into 8 squares. Ease each square into a prepared tin, allowing the corners to hang over the edges.
7. 7Fill each pastry-lined tin with the cooled lamb mixture up to the rim. Spoon the mashed potatoes on top, then fold the overhanging pastry corners over the potatoes. Whisk the eggs together, brush the pastry tops with egg wash, and sprinkle evenly with the Gruyere cheese.
8. 8Place the pies on a baking sheet and bake at 400°F until the pastry is golden brown (about 25–30 minutes). Let cool for 5 minutes, then divide evenly into 8 airt