Preheat oven to 350-degrees. Line a 13x9 pan with foil and apply nonstick spray.
Gently rinse the blueberries, removing any stems or smashed ones, and set the clean berries in a small bowl.
Using a mixer, beat the eggs and sugar for about 5 to 7 minutes, until pale in color and almost doubled in volume. The eggs are the leavening agent in this recipe, so it's important they are beaten until thickened, with the batter forming a ribbon as the beaters lift up.
Add the butter and vanilla, and mix for another two minutes. Measure out 1/2 cup of flour and carefully stir it into the blueberries to coat them, which will reduce sinking into the batter during the baking process. Slowly stir the remaining 1 1/2 cup of flour into the batter. By hand, gently fold the blueberries into the batter.
Pour batter into the ready pan. Bake for 40 to 50 minutes, until lightly browned and the center passes the toothpick test. Let cool completely before lifting up contents by the foil to slice into bars. Eat within two days, or freeze for later enjoyment.
OM NOM NOM!