Preheat oven to 350°. Mix together brown sugar and butter. Add egg and mix together. Add flour, salt, and vanilla, mixing together well. Spread dough onto cookie sheet to a thickness of 1/4 to 1/2 inch. Bake for 15 to 20 minutes, or until slightly brown. At this point, pull out of the oven and sprinkle chocolate chips evenly over the top (or 1/2 peanut butter chips and 1/2 chocolate chips). Return to oven for 1 minute. Remove and spread melted chips over the top. Cut into squares.
This is basically cookie dough, just spread out, hence the name "spreads" for the lack of a better name! Watch while baking that they don't get too browned, otherwise they will be dry. You can also use the packaged peanut butter cookie mix. Follow directions on back. Right before it's done baking, pour chocolate chips over it and put back in oven for 1 minute, then spread melted chips. VERY good!