Remove the parchment paper-lined cookie sheet from the oven and pour the mixture directly onto the warm parchment paper-lined pan in a rectangular shape (try not to dump it in one big mound or it may not spread as evenly). While wearing oven mitts, lift and tilt the various sides of the parchment paper in order to help the peanut brittle spread into a thin, even, and somewhat rectangular shape. Set aside to cool.