Preheat the oven to 350°F and line a 9×13 baking pan with parchment paper.
In a stand mixer, blend all shortbread crust ingredients until combined; don't worry if it seems dry. Press the dough evenly into the pan, using floured hands. Poke with a fork and par-bake for 18 minutes.
*For the crumble:*
While the crust is par-baking, whip up the crumble. In a food processor, combine dry ingredients and pulse three times.
Add cold, diced butter one piece at a time, pulsing until the mixture resembles wet sand (about 1 minute). Refrigerate until needed.
*For the blueberry filling:*
In a large bowl, mix all blueberry filling ingredients until evenly combined.
*For assembly:*
Once the crust is done par-baking, remove it from the oven. Spread the blueberry filling evenly, then sprinkle on the crumble.
Return to the oven and bake for 30-40 minutes, until the crumble is golden and the filling is bubbling.
Allow it to cool completely before cutting into 12 slices and serving!