Set the cream cheese out to soften, and the cool whip out to thaw. Then preheat oven to 350 F.
To a medium saucepan, add the fresh chopped rhubarb with 1 cup of water. Bring to boiling and cook the rhubarb until it's soft. Stir in the vanilla and sugar, reduce heat to low and simmer until it starts to burn off a little water. Make the cornstarch slurry by combining with the same amount of water. Pour the slurry into the rhubarb and let simmer for 5 minutes. It will thicken, then take the pan off the stovetop and set aside to let cool.
Combine the crushed pretzels, melted butter and sugar and press into the bottom of a 9x13-inch glass baking dish. Bake for 10 minutes, remove and let cool.
In a stand mixer or mixing bowl, combine the Cool whip and cream cheese with the sugar until smooth. Once the crust is cooled, carefully spread the creamy layer onto the pretzel layer.
Once the rhubarb has cooled, spread over the cream cheese layer. Cover with plastic wrap and refrigerate and let set for at least 2 hours.
Serve Rhubarb Pretzel "Salad" for dessert.