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1.Prepare and partially prebake the pastry shell: In the workbowl of a food processor fitted with the steel blade, pulse the flour, sugar, salt, and nuts until the nuts are finely chopped. Add the butter and shortening and pulse just until the mixture resembles coarse meal. Through the feed tube, add the yolk, lemon juice, and 1 or 2 tablespoons of ice water. Pulse a few times, stopping as soon as the dough begins to look clumpy. Add more water, 1 tablespoon at a time if needed, but do not allow a dough ball to form. Turn the clumpy dough out onto a piece of wax paper and gather it into a ball. Refrigerate it 30 minutes, or overnight, if time permits. Using a lightly floured rolling pin, roll out the dough until it measures about 1 inch larger around than the pie plate (set it on top of the dough to measure it). Fold the dough into quarters and fit it into the pie plate, positioning the folded point at the center. Unfold and gently drape the pastry over the pan; do not stretch it. Allow the dough to extend about 3/4 inch beyond the plate rim, then cut off excess. Fold under the extra dough, then pinch it up into points or flutes on the rim using your fingertips. Refrigerate the pastry-lined pan until the dough feels firm