Preheat oven to 350°.
In a medium bowl, whisk together flour, cornmeal, confectioners’ sugar, brown sugar, baking powder and salt.
Add melted butter, then use your hands or a wooden spoon to combine ingredients until a coarse little dough comes together, with no obviously dry spots.
Press ¾ of the cornmeal mixture into a 9-inch tart pan with a removable bottom, making sure the mixture is evenly pressed on the bottom and about ½ inch up the sides.
Place the shell on a rimmed baking sheet; pop the tart shell and remaining mixture into the fridge while you prepare the filling.
Toss blueberries, brown sugar, vinegar, flour and salt together in a medium bowl.
Pour the fruit into the crust.
Crumble the remaining cornmeal mixture over the blueberries, pressing bits of the mixture together into large clumps.
Bake tart until the blueberry filling is bubbly and thickened, and both the crust and top are nicely browned, 50–55 minutes.
Let tart cool completely before slicing into triangles and serving.
