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1
Special equipment: a wide 3-quart heavy flameproof casserole (about 2 inches deep; not glass); a potato ricer or a food mill fitted with medium disk Prepare filling: Blanch onions in a 2- to 3-quart pot of boiling salted water 1 minute, then transfer with a slotted spoon to a bowl of cold water to stop cooking.
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2
Drain onions and peel, trimming root ends with a paring knife.
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3
Wash leek slices in a bowl of water, agitating them, then lift out and drain in a medium-mesh sieve.
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4
Preheat oven to 350F.
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Pat lamb dry and sprinkle with 1 teaspoon salt and 1/4 teaspoon pepper.
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6
Put lamb and 3 tablespoons flour in a sealable plastic bag, then seal bag and shake to coat lamb.
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7
Melt 2 tablespoons butter in casserole dish over moderately high heat until foam subsides, then brown half of lamb, turning, about 6 minutes.
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Add 1 tablespoon garlic and cook, stirring, 2 minutes.
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9
Transfer browned lamb and garlic to a plate with a slotted spoon and repeat with remaining lamb and tablespoon garlic (do not add more butter).
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10
Add wine to casserole dish and deglaze by boiling over high heat, stirring and scraping up brown bits, 1 minute, then stir in tomato paste and boil, stirring, until liquid is reduced by half, about 5 minutes.
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11
Add broth, water, thyme, browned lamb with any juices that have accumulated on plate, onions, leeks, carrots, turnips, remaining teaspoon salt, and remaining 1/4 teaspoon pepper and stir to combine.
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12
Bring to a simmer over moderately high heat, then remove from heat.
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13
Cover dish with lid or foil and braise lamb and vegetables in middle of oven, stirring once or twice, until lamb is tender, 1 1/2 to 2 hours.
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14
Season with salt and pepper.
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15
Make topping while filling cooks: Peel and quarter potatoes.
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Cover potatoes with salted cold water by 1 inch in a 4-quart heavy pot, then simmer, uncovered, until very tender, 20 to 25 minutes.
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Drain in a colander.
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18
Bring cream, milk, and butter to a simmer in same pot over moderate heat, stirring occasionally until butter is melted, then remove from heat and stir in salt and pepper.
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19
Force hot potatoes through ricer into hot cream mixture and stir gently to combine.
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20
Keep warm, covered.
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21
Assemble and broil pie: Preheat broiler.
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22
Make a beurre manie by stirring together remaining 1 1/2 tablespoons butter and remaining 2 tablespoons flour in a small bowl to form a paste.
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23
Spoon 1 cup cooking liquid from casserole dish into a small saucepan and bring to a boil.
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24
Whisk in beurre manie, then simmer, whisking occasionally, until thickened, about 2 minutes.
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25
Gently stir sauce into lamb and vegetables.
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26
Spoon potatoes over lamb and vegetables and spread evenly with a fork, making a pattern with tines.
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27
Broil about 3 inches from heat until top is golden, about 3 minutes.
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28
Cooks' note: Lamb filling (without topping) can be made 1 day ahead and cooled, uncovered, then chilled, covered.
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29
Bring to a simmer over low heat before topping with warm potatoes and broiling.
