In a small bowl, combine pretzels and butter. Press onto the bottom and partially up the sides of a greased 9 or 10 inch springform pan. (I used a 9". The cheesecake comes right to the top of the pan if you choose to use a 9") Place on a baking sheet. Bake at 350 for 5 minutes. Cool on wire rack.
In a very large bowl, beat cream cheese and sugar until smooth. Add peanut butter and vanilla extract; mix well. Add eggs; beat on low until just combined. Stir in chips. Spoon over crust. Return pan to baking sheet.
Bake at 350 for 50-55 minutes or until center is almost set. Remove from oven; let stand for 15 minutes (leave oven on)
For topping - in a small bowl, combine sour cream, peanut butter and sugar. Spread over the filling. Sprinkle with chopped nuts. Return to the oven for an additional 5 minutes.
Cool on a wire rack for 10 minutes. Carefully run a knife around the edge of the pan to loosen; cool 1 hour longer. Refrigerate overnight. Remove sides of pan. Refrigerate leftovers.