Lemon Blueberry Streuseltaler

Streusel
39 Mix the flour, sugar, vanilla extract, and butter together with your fingers or a fork until it comes together into large crumbles.
Lemon Blueberry Filling
59 In a medium sauce pot, combine all of the filling ingredients. 
60 Cover the pot with a lid and place over medium high heat. Stir and check on the blueberries frequently. 
61 Once they begin to burst, remove the lid and reduce the heat to medium. Continue cooking and stirring until slightly thickened and reduced - about 10-15 minutes.
86 If using frozen blueberries, cook down to 300 grams.
87 Once cooked, transfer to a large shallow dish to cool to room temperature.
88 While they cook, start on the dough.
Dough
89 Combine flour, sugar and yeast in the bowl of a stand mixer and whisk together.
90 Pour in the milk, egg, butter, lemon zest, and vanilla.
91 With a dough hook, knead the mixture on low speed for 10-15 minutes until smooth. Shape the dough into a ball and place in a greased bowl that is at least twice the size of the dough, can be the same mixing bowl. Cover the bowl with a towel or plastic and place somewhere warm to rise for 45 minutes.
Shaping
93 Preheat the oven to 350 F. Arrange two racks in the oven so that they split the oven into 3 parts.
94 Once doubled in size, lightly sprinkle the dough with flour and punch out the air from the dough.
95 Weigh the dough and then divide the number by 9.
96 Use a bench scraper or your hands to divide the dough into 9 equal portions.
97 Shape each portion into a ball by gently flattening it out, and then tucking the edges under to create a taught surface. Roll the ball of dough in a clockwise direction under the palm of your hand on a clean work surface.
98 Always starting with the same piece of dough, roll each ball out into a circle that is about 4" in diameter and 1/2" thick.
Assembly
99 Transfer the disks onto two parchment (or silicone mat) lined baking sheets. Evenly divide the cooled blueberries onto each portion of dough.
100 Top the blueberries with large clumps of streusel. You should use up all of the streusel and make sure to cover the entire disk with berries and streusel - including the edges.
Bake
81 Let the streuseltaler rise for 20 minutes while the oven heats up. 
101 Bake the pastries for 15 minutes. Rotate and swap the baking sheets after 15 minutes, so they brown evenly, and bake for another 10-15 minutes until golden brown.
Final Steps
83 While they are baking, make the glaze by whisking together the powdered sugar and lemon juice. If needed add a little more lemon juice or powdered sugar until you reach the consistency of honey.
84 Once baked, remove the baking sheets from the oven and place on wire racks. Immediately drizzle the lemon glaze over the pastries.
85 Leave the pastries to cool for 10 minutes before consuming or transferring to a cooling rack to cool fully.