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1
Line rimmed baking sheet with foil. Mix 1/3 cup water and cream of tartar in small saucepan. Add sugar; stir over low heat until sugar dissolves. Increase heat; boil without stirring until golden, occasionally brushing down sides of pan with wet pastry brush and swirling pan, about 11 minutes. Add nuts; swirl to combine. Pour praline onto baking sheet, spreading with metal spatula. Cool.
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2
Break praline into chunks; grind half finely in processor. Reserve powder for filling and remaining chunks for garnish. (Can be made 5 days ahead. Store in airtight container at room temperature.)
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3
Blend flour, sugar, and salt in processor. Add shortening and butter; cut in using on/off turns until mixture resembles coarse meal. Transfer to medium bowl. Mix 2 tablespoons ice water and vinegar in small bowl and add to flour mixture. Stir until moist clumps form, adding more ice water by teaspoonfuls if dough is dry. Gather dough into ball; flatten into disk. Wrap in plastic; chill 45 minutes.
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4
Roll out dough on floured surface to 14-inch round. Transfer to 9-inch glass pie dish. Trim overhang to 3/4 inch. Turn edges under; crimp. Freeze 45 minutes.
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5
Preheat oven to 400u00b0F. Bake crust until edges begin to brown, pressing with back of fork if crust bubbles, about 12 minutes. Remove crust from oven. Reduce oven temperature to 350u00b0F.
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6
Whisk praline powder, pumpkin, and next 10 ingredients in medium bowl to blend.
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7
Pour filling into warm crust. Bake until filling is puffed around edges and just set in center, about 45 minutes. Transfer pie to rack; cool. (Can be made 1 day ahead. Cover loosely and chill.)
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8
Beat cream and sugar in bowl until peaks form. Transfer cream to pastry bag fitted with large star tip. Pipe rosettes around top edge of pie. Garnish with praline chunks.
