Lamb Shepherd's Pie with Puff Pastry

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  Ground Lamb(907g)
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  Yellow Onion
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  Carrots
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  Garlic
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  Thyme, Fresh(45g)
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  Low Sodium Beef Broth(600g)
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  Beer, Stout(340g)
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  1 teaspoon sea salt
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  ½ teaspoon freshly cracked black pepper
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  Cornstarch(45g)
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  Peas, Sweet, Frozen(240g)
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  Puff Pastry Dough, Frozen, Thawed
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  Egg, Whole, Large(50g)
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  Cheese, Gruyere(240g)
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  Potato, Russet, Baked, Flesh Only
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  1 teaspoon sea salt
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  Cream, Heavy Whipping(60g)
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  Unsalted Butter(60g)
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  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 eight oven proof cocottes.
2. 2In a large skillet over medium heat, cook the lamb, breaking it up with a spoon until browned. Using a slotted spoon, transfer the meat to a plate. Drain off all but 2 tablespoons of fat from the pan. Stir in the onions and carrots, and cook until the onions are translucent, about 5 minutes. Add the garlic and cook until fragrant, 1 minute longer. Add the meat back to the pan along with the thyme, stock, beer, salt and pepper, stirring to combine. Cover with a lid and place in the oven for 1 hour.
3. 3In a small bowl whisk the cornstarch into 4 tablespoons of cold water until dissolved. Remove the meat mixture from the oven and stir in the cornstarch mixture until combined. Stir in the peas then return the dish to the oven until the sauce has thickened, about 30 more minutes. Remove the meat mixture from the oven and let it cool completely before filling the pies (to prevent the pastry from becoming soggy).
4. 4Meanwhile, bring a large pot of salted water to a boil over high heat. Add the potatoes and cook until just fork tender, about 15 minutes. Drain.
5. 5In the pot used for the potatoes, combine the cream and butter over medium heat. Cook, stirring, until the butter is melted, about 2 minutes. Using a potato ricer, rice the potatoes over the hot butter mixture (Alternatively, mash the potatoes directly in the liquid, taking care to not overwork them). Season with remaining salt and pepper.
6. 6Increase the oven temperature to 400°F.
7. 7On a lightly floured surface, roll the pastry to ⅛ inch thick. Using a sharp knife, cut into 8 squares (avoid stretching the dough to prevent the edges from not puffing). Ease the pastry squares into the prepared pie tins. The four corners of each pastry square will hang over the edge of each tin.
8. 8Fill the pastry lined tins with the meat mixture up to the rim. Using a spoon or a pastry bag, spread the potatoes on top of the meat filling and fold the overhanging pastry corners on top of the mashed potatoes. Using a pastry brush, brush the top of the pies with the egg and sprinkle evenly with the cheese.
9. 9Place the pies on a baking sheet and bake until the pastry is golden brown, about 25-30 minutes.