For the crust:
2 1/2 cups flour
1 cup (packed) crumbled plain halvah (about 7 ounces)
2 tablespoons sugar
1/2 teaspoon salt
3/4 cup (1 1/2 sticks) chilled margarine or shortening, cut into small cubes
2 large egg yolks
2 tablespoons ice water
For the filling:
2 cups sugar
1/2 cup water
1/2 cup whipping cream (topping)
¾ cup canola oil
1 cup natural unsalted pistachios (about 4 ounces), toasted
Nonstick vegetable oil spray
1 large egg white
1/2 cup whipped topping
8 ounces bittersweet or semisweet chocolate, chopped
1 tablespoon light corn syrup
Prepare the crust:
Combine flour, halvah, sugar, and salt in processor. Using pulses, process until blended to sandy texture. Add margarine or shortening. Keep pulsing until mixture resembles coarse crumbs. Whisk egg yolks and 2 tablespoons ice water in small bowl to blend. Add to flour mixture. Again pulsing, process until moist clumps form. Gather dough into 2 balls; flatten into disks. Wrap separately in plastic. Chill 1 hour.
Combine sugar and 1/2 cup water in heavy large saucepan. Stir over medium heat until sugar dissolves. Increase heat to high and boil until syrup turns deep amber or clip-on candy thermometer registers 360 degrees F, occasionally swirling pan and brushing down sides with wet pastry brush, about 11 minutes (time will vary depending on size of pan). Remove from heat. Carefully stir in cream (mixture will bubble). Add oil and whisk until smooth. Stir in pistachios. Cool until lukewarm but still pourable, about 30 minutes.
Meanwhile, preheat oven to 350 degrees F. Lightly spray 9-inch-diameter tart pan with removable bottom with nonstick spray. Roll out 1 dough disk between 2 sheets of parchment paper or waxed paper to 11-inch round (dough will be about 1/3 inch thick). Remove top paper. Invert dough into prepared pan. Remove remaining paper. Trim dough overhang.
Roll out second dough disk between 2 sheets of parchment paper or waxed paper to 10-inch round. Pour filling into prepared crust. Brush edges of crust with egg white. Remove top paper from second dough disk. Invert over filling. Remove paper. Be sure to press dough around pan until the edges to trim and seal.
Place torte on baking sheet and bake until crust is golden, about 35 minutes. Cool completely in pan. Chill overnight.
Bring cream just to boil in medium saucepan. Remove from heat. Add chocolate and corn syrup; whisk until smooth. Cool 5 minutes.
Remove sides from tart pan. Invert tart onto rack. Remove bottom of tart pan. Pour warm glaze over tart (bottom of tart becomes top). Let stand until glaze sets. (Can be made 3 days ahead. Cover and refrigerate. Let stand at room temperature 1 hour before serving.)
Slice into thin wedges and serve.