Crank oven to 300 degrees F.
Lube an 8-inch square baking pan with non-stick spray. Trim a piece of parchment paper so that it fits just inside the baking pan with 2-inch overhang on two sides and place it inside the pan. This is essentially a sling that will allow for easy removal.
Beat the eggs with a stand mixer fitted with the paddle attachment at medium speed until fluffy and light yellow, 2 to 3 minutes.
Sift together the granulated sugar, brown sugar, cocoa powder, flour and salt into a separate bowl. Reduce the mixer speed to low and slowly introduce the sugar mixture followed by the butter and vanilla. Mix until just smooth and pour into the prepared pan.
Bake for 15 minutes, then remove from the oven and cool for 15 minutes. Then, return the pan to the oven and bake until an instant-read thermometer inserted into the middle of the brownie reads 195 degrees F (approximately 30 minutes).
Cool in the pan for 30 minutes, then transfer the brownie to a cooling rack for 10 minutes before cutting into 16 pieces using a pizza wheel or long slicer.
I'd tell you how to store them by stacking them in an airtight container, separating the layers with wax paper, but you know good and well that isn't going to happen? Don't you?