FOR THE SHELL:

1 1/4 c. unbleached all-purpose flour
1/3 c. chilled vegetable shortening
3 tbsp. ice water

FOR THE FILLING:

3 lg. eggs
1/3 c. firmly packed light brown sugar
1 c. fine-quality maple syrup or 1 c. light corn syrup
1 tsp. cider vinegar
1/2 tsp. vanilla or, if using corn syrup, 1/4 tsp. natural maple flavor (available at specialty foods shops and many supermarkets)
3 tbsp. unsalted butter, melted and cooled

1 c. coarsely chopped black walnuts
Whipped cream as an accompaniment

Make the shell: In a bowl stir together the flour and a pinch of salt; blend in the shortening and blend the mixture until it resembles meal. Add the ice water; toss the mixture until the water is incorporated, and form the dough into a ball. Chill the dough, wrapped tightly in plastic wrap, for 30 minutes.

On a lightly floured surface roll out the dough into a 10-inch round, transfer it to an 8-inch pie plate, trimming the edge, and crimp the edge decoratively. Chill the shell for 1 hour.

Make the filling while the shell is chilling: In a large bowl beat the eggs until they are frothy. Add the brown sugar, and beat the mixture until it is smooth. Beat in the maple syrup, the vinegar, the vanilla, and a pinch of salt, beating until the mixture is smooth, and beat in the butter.

Spread the black walnuts evenly on the bottom of the shell, pour the filling over them and bake the pie in the lower third of a preheated 375 degree oven for 35 minutes. (The center of the pie will not be completely set, but it will continue to set as the pie cools.)

Transfer the pie to a rack and let it cool to room temperature. The pie may be made 1 day in advance and kept covered and chilled. Let the pie return to room temperature before serving. Serve the pie with the whipped cream.