1. 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.
2. 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.
Tips: This tart can be made dairy for other occasions by using milchig cream cheese, heavy sweet cream instead of the whipping cream, and butter in place of the margarine.