These taste JUST like a Reese's Peanut Butter Cup and are so easy to make! There are a lot of similar recipes, with slightly different amounts of (mostly) the same ingredients, but this is the one that I really like.
Mix butter, graham cracker crumbs, powdered sugar, and peanut butter. (an easy way to measure the peanut butter is to put 1 cup of water into a measuring cup, and then add enough peanut butter to it that the water reaches 2 cups).
Press mixture into a 9x13" pan.
Melt chocolate chips in microwave and stir until smooth (try a minute first, and then check).
Spread chocolate carefully over peanut butter layer with a spatula. (Having one person to pour the chocolate and one to spread works well!).
Let the chocolate cool for a while, and then cut into bars before the chocolate is completely hardened (or else the chocolate layer will just crack).
(cooking time is cooling time, and it's a very rough estimate, I didn't keep track).