Preheat oven to 350 degrees. Have an 8- or 9-inch pie plate at hand.
Place the unbaked pie shell in the pie plate. Sprinkle the bottom of the pie shell evenly with chocolate chips.
Whisk together the eggs, sugar and flour in a mixing bowl.
Gradually mix in the melted butter, then add the nuts and vanilla.
Carefully pour the mixture over the chocolate chips, in a circular motion so it does not disturb the chips.
Bake for 1 hour, until the filling is set.
Serve slightly warm, with whipped cream if desired.