Preheat your oven to 425° F.
Place a sheet of puff pastry on a flat surface and begin rolling it out with your rolling pin. To avoid having the pastry stick to your surface, flip it at least once. You should have a 9 x 11 inch rectangle.
Sprinkle 1 tbsp of sugar over the puff pastry and impress them into the dough by using your rolling pin. Flip and repeat.
Using a sharp knife, score all around the dough, one inch from the edge (so that you have a rectangle within a rectangle--refer to photograph or video). Make sure not to actually cut the dough.
Place the puff pastry on a baking sheet lined with parchment paper and bake in the oven for 10 minutes.
While the puff pastry is baking, microwave the raspberry preserves for 30 seconds. They should be very runny.
Add the melted preserves to your fresh raspberries and stir until the berries are evenly coated.
Add 1 tbsp of sugar to your blueberries, together with lemon juice. Stir.
When the puff pastry is golden brown, remove from the oven. Gently tap the center of the sheet with the back of a spoon and press it down.
Pour the raspberries into the center and spread them out. Next, add the blueberries.
Top with a little whipped cream and serve.