Stir together flour, cornmeal, and a pinch of salt and set aside.
Cream softened butter and sugar in a bowl until it is light and fluffy, then add vanilla and mix.
Add dry ingredients on low speed being careful to scrape the sides of bowl several times.
Stop mixing when ingredients are fully incorporated but dough is still crumbly.
Evenly distribute 1 1/2 cups of the crumbly dough over bottom of prepared pan and press lightly to hold in place.
Put the remaining dough in the refrigerator.
Bake crust for 25 minutes, or until lightly toasty brown.
Spread 1 1/2 cups blueberry filling over crust and crumble the remaining dough over the top of filling.
An even covering will produce a crust that covers blueberries almost entirely, letting it peak through here and there.
Put back in oven and bake until top crust is golden brown, about 40 minutes, rotating the pan halfway through the baking time.
Remove from oven and cool on a rack for 10 minutes then carefully run a knife around the edge of the pan to prevent the bars from sticking.
Cool completely and cut into bars.