Last night I was asked to upsize a home brownie recipe to a full sheet size. I've done a few full sheet cakes, but never brownies. I used a 300f oven on low fan, frame. I set an upside down sheet pan on the frame to slow baking down (mistake?). By the time the center was slightly wobbly the edges were burnt. Easy enough to trim, but how could I have avoided this? Maybe wide foil on sides leaving only a small patch uncovered in the center? Half sheets?