For Chocolate Pastry: In a food processor, combine flour, cocoa powder, brown sugar and salt. Cover; process until just combined. Add butter. Cover; process with on/off turns until butter pieces are pea-size. With processor running, quickly add water through feed tube until dough just comes together.

Transfer mixture to a large mixing bowl; gather flour mixture into a ball, kneading gently until it holds together. Gently pat dough into a disk.

On a lightly floured surface, roll the dough from center to edges into a 12-inch circle. Wrap pastry circle around rolling pin; unroll into a 9-inch glass pie plate. Ease pastry into pie plate without stretching it. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry even with edge of plate. Crimp edge as desired. Using a fork, prick the bottom and side of the pastry shell, being sure to prick where bottom and sides meet. Line pastry with a double thickness of foil.

Bake in a 450°F oven for 8 minutes. Remove foil. Bake for 6 to 8 minutes more or until pastry is set and looks dry. Cool on a wire rack. Set baked pie pastry shell aside.

For filling: In a medium heavy saucepan, combine the whipping cream, chocolate and granulated sugar. Cook and stir over medium heat about 10 minutes or until mixture comes to boiling and thickens. (If chocolate flecks remain, use a wire whisk to beat mixture until blended.)

Gradually stir about half of the hot mixture into egg yolks. Return egg yolk mixture to saucepan. Cook and stir for 2 minutes. Remove from heat; stir in espresso and vanilla. Cool slightly. Pour warm filling into the baked pie pastry shell. Cover and chill for 8 to 24 hours or until filling is set.

To serve, cut into wedges and top each serving with whipped cream. If you like, garnish whipped cream with chocolate curls and espresso beans.