Grease a 9-inch springform pan, and line with parchment paper or wax paper; grease paper. Set aside.
Combine chocolate morsels and butter in the top of a double boiler; bring water to a boil. Reduce heat to low; cook until chocolate and butter melt, stirring occasionally. Remove from heat; add liqueur, beating with a wire whisk until blended. Set aside, and let cool.
Combine eggs, 1/4 cup sugar, 1 tsp vanilla, and salt in a large mixing bowl. Beat at high speed of an electric mixer 5 minutes or until the mixture triples in volume. Sprinkle flour over the egg mixture and gently fold together. Fold in reserved chocolate mixture. (The batter will decrease in volume).
Pour the batter into your prepared pan. Bake at 400°F for 10 to 12 minutes or until the center is firm but not set. (DO NOT OVERBAKE). Cool to room temperature in the pan on a wire rack. Cover and chill for at least 8 hours.
To serve, carefully remove the sides of the springform pan. Beat whipping cream and 1/2 tsp vanilla until foamy; gradually add sifted powdered sugar, beating until soft peaks form. Serve on top of your cake slices. Or, if you want to present the cake whole, gently spoon the whipped cream mixture into a decorator bag fitted with the desired tip. Pipe the whipped cream mixture on top of the pie.