In a food processor combine walnuts, peanut butter pieces, and chocolate pieces. Cover and process until mixture is coarsely chopped (or coarsely chop nuts, peanut butter pieces, and chocolate pieces with a knife and combine). Transfer mixture to a large bowl; set aside.
In a small heavy saucepan combine brown sugar, corn syrup, and butter. Bring to boiling over medium heat, stirring constantly. Stir in sweetened condensed milk. Return to boiling over medium heat, stirring constantly. Reduce heat to medium-low. Clip a candy thermometer to side of pan. Continue cooking, stirring constantly, until mixture reaches 236 degree F, soft-ball stage (should take about 10 minutes). (Adjust heat as necessary to maintain a steady boil.) Remove saucepan from heat; stir in vanilla. Cool 15 to 20 minutes or until slightly thickened.
Dip each pretzel into caramel mixture, covering about 2/3 of the pretzel. Let caramel drip off slightly. Spoon or roll some of the crumb mixture onto the caramel, pressing crumbs lightly into caramel with back of a spoon. Let stand on nonstick foil until caramel is set. Store in an airtight container between layers of wax paper in refrigerator up to 4 days or freeze up to 1 month. Makes 25 pretzel rods or 15 whole Bavarian pretzels.