While the dough is rising, make the filling. Over the stove on medium heat, combine the blueberries, granulated sugar and lemon juice, constantly stirring until the blueberries get softer, about 2-3 minutes
Using the back of a wooden spoon, smash the blueberries so that they release their juices. Let the mixture simmer, while stirring occasionally, until thickened, about 5-10 minutes. Remove from the heat and let cool while the dough completes its first rise.
Once the dough has finished its first rise, grease a muffin tin or line a baking sheet with parchment paper (both work) and set aside. Remove the dough from the bowl onto a lightly floured surface.
Using a rolling pin, roll out the dough into a 16x20 inch rectangle.
Spread the filling on the right ⅔ of the rectangle.
Then, take the left ⅓ that is not covered in filling, and fold it towards the center.
Then, take the right side and fold it over towards the center. It is like you have a piece of paper and you are folding it to get three equal-sized parts.