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1
Put oven rack in middle position and preheat to 375u00b0F.
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2
Pulse flour, sugar, and salt in a food processor until combined. Add butter and zest and pulse until mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Add yolks, vanilla, and water and pulse just until incorporated and dough begins to form large clumps.
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3
Turn dough out onto a work surface and divide into 4 portions. Smear each portion once with heel of your hand in a forward motion to help distribute fat. Gather dough together using scraper and form into a ball, then flatten into a rectangle.
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4
Put dough in tart pan and pat out with well-floured fingers into an even layer over bottom and up sides so it extends about 1/4 inch above rim. Chill 30 minutes.
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5
Lightly prick tart shell all over with a fork, then line with foil and fill with pie weights. Bake shell until golden around edge, about 15 minutes. Carefully remove foil and weights and bake until shell is golden all over, about 15 minutes more. Cool shell completely in pan on a rack. Leave oven on.
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6
Beat together almond paste, butter, sugar, and almond extract in a bowl with an electric mixer at medium-high speed until creamy, about 3 minutes. Reduce speed to low and add eggs, 1 at a time, beating well after each addition, then mix in flour and salt.
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7
Halve nectarines, discarding pits, then cut into 1/4-inch-wide wedges.
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8
Spread frangipane filling evenly in tart shell. Stand nectarine wedges, skin sides down, decoratively in filling, being careful not to push too far into filling.
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9
Bake tart until frangipane is puffed and golden and edges of nectarines are golden brown, about 1 1/4 hours.
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10
Heat preserves and water in a 1-quart saucepan over moderately high heat, stirring, until preserves are melted. Remove from heat and force through a fine-mesh sieve into a small bowl, discarding solids. Stir in Amaretto (if using).
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11
Brush top of hot tart generously with glaze and cool in pan on rack 15 minutes. Remove side of pan and cool tart completely, about 2 hours.
