Preheat the oven to 350 degrees F. Lightly butter the bottom and sides of a 10-inch pie plate. In a large bowl, combine the wafer crumbs and margarine. Press the mixture firmly against the bottom and sides of the pie plate. Bake for 8 minutes. When the crust is cool, spread ½ cup of the cherry pie filling evenly over the bottom and chill. Refrigerate the remaining filling until serving time.
In a medium-size saucepan, combine the sugar and gelatin; mix well. Add the water and white baking bar. Bring to a boil over medium heat, stirring constantly, and cook until the gelatin is completely dissolved. In a small bowl, beat the egg yolks. Add 1 cup of the hot gelatin mixture to the yolks and quickly stir until combined. Return to the saucepan and cook over medium heat, stirring constantly, until the mixture bubbles. Transfer the gelatin mixture to a large bowl. Chill in the refrigerator, stirring occasionally, for 45 minutes, or until it is the consistency of unbeaten egg whites. Do not let it get too firm.
Meanwhile, in the chilled bowl of an electric mixer, beat the cream until stiff peaks form. Add the liqueur. Gently fold into the chilled gelatin mixture. Pour into the crust. Cover and refrigerate overnight. Just before serving, spoon the remaining cherry filling evenly over the pie and garnish with whipped cream and chocolate shavings if desired.