Add pretzel crumbs and brown sugar to spring-pan. Add melted margarine. Stir crumbs until incorporated with other ingredients. Press onto bottom of pan. Bake at 350°F for 15 minutes.
On parchment add the 1½ cups of pretzel pieces. Pass melted chocolate over them to cover. Stir them around to coat well. Place in refrigerator.
Beat cream cheese well. Add sugar, flour, and vanilla. Mix at medium speed, add eggs 1 at a time on low speed, just until blended. Add sour cream on low. Fold in chocolate covered pieces by hand. Bake over water bath at 325F for 1 hour and 5 minutes. Run knife around rim of pan to loosen cake. Let cool before removing rim. Refrigerate 6 to 8 hours.