Preheat oven to 350 degrees and grease a 9 x 13 pan.
In a food processor fitted with the "S" blade, pulse the crust ingredients through the butter. Alternately, you could use a pastry cutter or your fingers to work the the fat into the dry ingredients until it is well dispersed and no bigger than small peas.
When well combined, add the vanilla and the milk, 1 tablespoon at a time, and pulse a few times to mix. Stop adding milk when the dough can be pressed together with your fingers. HINT: If you like a softer dough, add a bit more milk, if you prefer more crunch, don't!
Press 1/2 of the dough into the bottom of a 9 x 13 pan (I used my Silpat so it did not stick to my hands).
Mix the blueberries, sugar, and tapioca flour together.
Spread this over the crust, and crumble the remaining cookie crust over the top.
Bake in a 350 degree oven for about 45 minutes until the crust is golden and the center is set. Let cool before cutting.