Thoroughly cream room-temperature butter with sugar. Blend in melted chocolate and vanilla. Add eggs one at a time, beating 5 minutes after each addition. Pour into cooled pie shell and chill 2 hours before serving. Top with whipped cream, then sprinkle walnuts over the top.
Remember you can substitute 3 tablespoons of cocoa plus 1 tablespoon cooking oil if you do not have any bakers squares on hand.