Line your baking tray with parchment paper and set aside. Remove puff pastry from freezer and allow to thaw in the fridge for at least one hour before beginning. If you have instructions on your puff pastry packaging for thawing, use this.
1 sheet frozen puff pastry
In a medium sized bowl, add flour, sugar, and cold butter. Using your hands, mix this until crumbly and combined. Set in the fridge while you make the jam.
3 tbsp butter, 3 tbsp white sugar, 1/2 cup flour
Mix together water and cornstarch, making sure there are no clumps. Then in a pot over low heat, add the fresh blueberries. Allow it to simmer for 1-2 minutes, mixing the entire time. Add in the cornstarch water mixture and mix for another 1-2 minutes until it's thickened up. Turn the stove off and transfer the jam to a bowl to cool.
1 tbsp water, 1 tbsp cornstarch, 1 1/2 cups fresh blueberries
Preheat the oven to 350℉. Unfold the thawed pastry and place on the tray. Cut it into 4 even rectangles. Then cut each rectangle in half, making 8 total. 4 will be for the bottom, and the other 4 for the top.
Add 1-2 tbsp of the jam onto each of the 4 rectangles. Make sure to leave a 1 cm border all around.
Take the puff pastry pieces and place on top. Then take a fork and firmly press down, combining the two together. Make sure it is sealed correctly or else the jam will leak out (Some of mine did leak out!).
Add a heaping amount of streusel on top of each danish.
Bake the danishes for 20-25 minutes at 350°F. They will be ready when the puff pastry has risen and is nice and golden. If you want your streusel to be golden brown, set your oven to broil for 1-2 minutes after baking the danishes.
Optional: Whip 35% heavy whipping cream (Or used store-bought) and then place on top of the danishes along with some more leftover blueberry jam. Enjoy!
whipped cream