Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Place pretzels, brown sugar, and salt in a food processor fitted with the knife attachment. Finely grind together. Transfer to a bowl and add melted margarine. Mix together. Press evenly on bottom and partway up the sides of a nine-inch tart pan with removable bottom. Bake for 18 minutes. Set aside to cool.

Place pareve cream cheese and peanut butter in the bowl of a mixer and beat until soft and fluffy, about one minute. Add brown sugar and beat until combined. In a separate bowl beat whipping cream with vanilla until soft peaks form. Don’t overbeat. With a whisk, fold peanut butter mixture into whipped cream mixture. Spread evenly in tart shell and cover with plastic wrap. Refrigerate for three hours.

Place sugar, corn syrup, and water in a small, heavy saucepan. Over medium flame, stir constantly until sugar dissolves and syrup starts to bubble. Once it starts bubbling, lower flame to small/medium, stop stirring, and let mixture caramelize on its own until it reaches a deep amber color. This takes approximately 20 minutes.

Remove from heat and add the pareve whipping cream slowly and carefully because it can bubble up furiously. Use a wooden spoon to stir mixture until smooth, scraping up the thicker part that settles on the bottom. If any lumps develop, return pan to heat and stir until dissolved. Stir in the margarine and transfer to a bowl to cool. When just slightly warm, add the vanilla extract and stir. Drizzle caramel over tart and return to fridge until ready to serve.