Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius) for 20 minutes.
Spray an 8-inch square (or snowflake) baking dish liberally with baking spray. Set aside.
Whip the eggs in a large bowl on high speed for at least 3 minutes until light and frothy.
Add the sugar, vanilla, and salt to the bowl and continue whipping at high speed for an additional 2-3 minutes. *Note - The whipping is what will give rise to the cookie bars as they bake so don't skip this step.
Beat the flour into the egg and sugar mixture, one cup at a time, starting on low speed and increase the speed gradually until the flour is fully incorporated, being careful not to overbeat. Scrape down the sides of the bowl as needed with a rubber spatula.
Add the batter (it will be thick) into the prepared baking pan and smooth the batter evenly with the spatula throughout the surface of the pan.
Bake the in a preheated oven for 40-45 minutes, or until a cake tester or toothpick inserted into the center of the baked dough comes out clean.
Cool on a wire rack for at least 10 minutes and then carefully turn the cookie out onto a wire rack to continue cooling.
Once fully cooled, sprinkle the top of the cookie bar liberally with confectioners' sugar (optional) and cut into squares or wedges depending on the baking pan used.