Preheat oven to 350 degrees F (175 degrees C). Generously grease a 9 inch springform pan with 2 3/4 inch sides.
In a medium bowl, mix together crushed cookies and softened butter or margarine. Press mixture evenly into greased pan. Bake in preheated oven for 5 minutes, then allow to cool.
Combine 1 cup cream, chocolate, vanilla extract, and salt, in the top of a double boiler. Heat until chocolate is fully melted and mixture is smooth. Alternatively, if you have a food processor, you can blend mixture by placing chocolate, vanilla extract, and salt, in processor bowl. Bring 1 cup cream to a boil on stovetop, then slowly pour cream into processor with blade running. Continue to process until mixture is smooth.
Pour chocolate mixture into a bowl and cool to room temperature, stirring occasionally.
In a large bowl, beat 2 cups chilled cream with 1/4 cup sugar. Beat until stiff peaks form. Fold whipped cream into chocolate mixture. Pour mixture into cooled crust.
Chill pie at least 6 hours before serving. Prior to serving, beat remaining 1 cup cream with 1/4 cup sugar. Beat until stiff, then pipe onto top of pie with a star tip, or place a spoonful on top of each slice.