Preheat oven to 350°F. With a mixer, beat eggs with the sugar until slightly thickened and light in color, about 5-7 minutes. The mixture should almost double in size. Add butter and vanilla; mix two more minutes. Stir in the flour until just combined. Add the blueberries and stir by hand to mix throughout.

Spread in a buttered 9x13 pan. Bake 40-50 minutes, or until very lightly browned and a toothpick inserted in center comes out clean. Cool completely before cutting into small squares.