Preheat oven to 350 degrees F. Grease 13- x 9-inch baking dish or pan.
In a large bowl, mix together the oatmeal, brown sugar, butter, Karo syrup, and vanilla extract until well blended.
Firmly press dough into prepared baking dish or pan and bake for 15 minutes only. NOTE: Do not overbake or the cookie base will turn rock hard. Remove from oven and let cool.
In a saucepan over low heat, melt chocolate chips and peanut butter, stirring to blend. Remove from heat.
Spread warm chocolate/peanut butter mixture over the cooled cookie base. Refrigerate at least 1 hour. After 1 hour, cut into bars or squares.
Makes 2 dozen bars.
Oh Henry Bars Cookie Recipe: https://whatscookingamerica.net/cookie/ohhenrybars.htm