For filling, beat cream cheese, sugar and 2 tablespoons vanilla in large bowl until well blended. Beat in sour cream. Add eggs, 1 at a time, beating after each addition. Add 1 1/2 cups crushed Butterfingers. Pour into pan. Bake about an hour, until golden on top, cracked on edges and set a little in the center. Transfer to rack. Let cool.
Meanwhile, coarsely chop chocolate and place in medium bowl. Heat cream. When it begins to boil, pour over chocolate. Let sit 1 minute, then stir until smooth.
Take one-third of the mixture and put into plastic zip bag. Set aside. Put the remaining two-thirds in the refrigerator for about 10 minutes to thicken. Remove and spread over cake. Then sprinkle remaining 1/4 cup Butterfingers over the glaze. Finally, drizzle remaining chocolate from the plastic bag over the top. Refrigerate overnight.
Makes 12 servings.