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1
Blend first 4 ingredients in medium bowl. Add butter and shortening and rub between fingertips until mixture resembles coarse meal. Add vanilla. Mix in enough water by tablespoons to bind dough. Gather dough into ball; flatten into disk. Wrap in plastic. Refrigerate at least 30 minutes. (Can be prepared 1 day ahead. Soften slightly at room temperature before continuing.)
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2
Roll out dough between sheets of lightly floured waxed paper to 1/8-inch-thick round. Peel off top sheet of paper. Trim dough to 12-inch round. Transfer to 9 1/2-inch deep-dish glass pie dish; discard paper. Trim overhang to 1/2 inch. Crimp edges. Refrigerate 20 minutes. (Optional garnish: Gather dough scraps and roll out on lightly floured surface to thickness of 1/8 inch. Cut out fourteen 3-inch-long leaves with knife or cutter. Refrigerate leaves until ready to use.)
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3
Position rack in bottom third of oven and preheat to 350u00b0F. Line crust with parchment paper or foil. Fill with dried beans or pie weights. Bake until crust is set, about 15 minutes. Remove paper and beans. Brush crust bottom and sides (not edge) with some of glaze. Sprinkle with 2 tablespoons oats. Bake until light brown, about 20 minutes. Cool completely.
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4
Increase oven temperature to 375u00b0F. Combine 2/3 cup oats, flour, sugar, and cinnamon in processor. Add butter and cut in until crumbly. Transfer mixture to medium bowl. Stir in remaining 2 tablespoons oats.
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5
Mix rhubarb, strawberries, sugar, cornstarch, cinnamon, and nutmeg in heavy large saucepan. Let stand 30 minutes. Bring to boil over medium heat, stirring constantly. Reduce heat and simmer until juices thicken, about 3 minutes.
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6
Pour filling into prepared crust. Cover with topping. Bake 20 minutes. (If using pastry leaves, remove pie from oven and quickly arrange leaves around edge, overlapping slightly. Brush leaves with glaze.) Bake until topping and leaves are golden and juices bubble, about 15 minutes longer. Cool on rack. Serve warm or at room temperature.
