Preheat oven to 400 degrees F. Line a rimmed baking sheet with parchment paper.

Remove the thawed puff pastry from the fridge and lay the sheet out flat on a floured work surface. Use a rolling pin to roll it out so the final size is rectangle about 12"x15". Place the sheet of puff pastry on the prepared sheet pan. 

Then, spread on a very thin layer of the organic strawberry preserves/jam to act as a "glue." Begin arranging the fresh raspberries and rhubarb diamonds on top of the jam in whatever pattern you like. Be sure to leave about an inch frame of dough around the edges so there isn't much leakage. Rhubarb is very geometric, so you can get creative with the pattern. Then, generously sprinkle on some sugar over the fruit and on the borders. 

Bake at 400 degrees F for about 25-30 minutes, until the edges are very golden brown, and the rhubarb is soft. The tart will be juicy, but once it cools, the juices will thicken. While the tart is cooling, combine the cold heavy whipping cream, sugar, and vanilla extract in the bowl of an electric stand mixer, or a large bowl with a handheld mixer. Beat on medium speed for about 4-5 minutes until soft peaks form. Slice up the tart into large squares, and top each piece with a generous spoon of whipped cream.