In food processor add 3 cups flour and 1 teaspoon salt. Pulse the mixture a few times. Add 1 cup slices of butter. Pulse about 20 times. Add 3 tablespoons ice water in a steady stream from the top of the processor, while you pulse the mixture. Continue until just before the dough forms a ball.
Remove the dough from the processor and form into a ball, mixing it with your hands for about 2-3 seconds. Divide the dough into 2 equal parts.
Melt chocolate in a double boiler. In a separate bowl, mix together the egg yolks and sugar.
Add two tablespoons of melted chocolate into yolk mixture to temper it. Then add yolk mixture to the rest of the chocolate and cook over a double broiler for 2 to 3 minutes.
Add 1 tablespoon liqueur, stir in completely. Remove mixture from double broiler and set aside to cool.
Whip 6 egg whites with a pinch of salt until it forms stiff peaks. Place the chocolate mixture into a large bowl at room temperature. Then fold the whipped egg whites into the cooled chocolate mixture, putting in one-quarter to start. Gently fold in the rest.
Pour mixture into the cooked backed pie shell. Chill overnight.
Serve topped with whipped cream.