In a medium bowl, blend together softened butter, 2 cups flour and 1/2 cup sugar. Press into the bottom of an ungreased 9x13 inch pan.
Bake for 15 to 20 minutes in the preheated oven, or until firm and golden. In another bowl, whisk together the remaining 1 1/2 cups sugar and 1/4 cup flour. Whisk in the eggs and blueberry juice. Pour over the baked crust.
Bake for an additional 20 minutes in the preheated oven. The bars will firm up as they cool.