Thaw ice cream for an hour or two.
Crush pretzels in a bag until they are all small crumbs.
Mix butter, sugar, and pretzel crumbs in a bowl.
Pour pretzel mixture into an 8 inch springform pan and press down firmly (I used a flat bottomed ramekin to press to bottom and against sides) along the bottom and up about 1 inch on sides.
Melt 1/4 cup peanut butter in glass bowl in microwave for 15-20 seconds. Mix in 2 ounces of chopped chocolate and microwave for an additional 15-20 seconds. Stir until no chocolate chunks.
Pour and spread peanut butter chocolate mixture over the pretzel crust.
Place in freezer for 10-15 minutes to harden.
Melt the remaining chocolate and peanut butter in the microwave using the same directions as above.
Mix in 2/3rds of this chocolate peanut butter mixture into the ice cream.
Spread into pretzel crust, drizzle top with remaining melted chocolate and peanut butter, and freeze for at least 2-3 hours before serving.
Top with crushed pecans and whipped cream if desired.