Heat oven to 375. Place the pie plate on a baking, line with piecrust (homemade or store-bought). Prick crust with fork and line with foil. Fill to top with pie weights or dried beans (I use rice). Bake until edges are firm, 20-25 minutes. Remove the foil and weights and bake until just golden, 8 to 10 minutes (I cover the edges with a pie shield because you need to bake it again with the chocolate filling).
Reduce oven temperature to 325°F Combine the butter and chocolate and melt (over a sauce pan--not in--of simmering water or in the microwave, being careful not to burn).
Using an electric mixer, beat the eggs, salt and 1/2 cup sugar until fluffy, 4-5 minutes. Fold of third of the egg mixture into the chocolate mixture, then fold in the remainder.
Pour the combined mixture into the crust and bake until puffed and beginning to crack, 20 to 25 minutes. Cool for 1 hour, then chill.
Beat the heavy cream with 3 TBL sugar until soft peaks form. Spread over the pie and sprinkle with shaved chocolate, if desired.