Bring to boil on med-high heat until bubbles form. Bubble for about 30 seconds.
Remove from heat & stir in peanut butter & vanilla
Pour over cereal mixture & combine
Stand a few minutes till just about room temperature & then stir in chocolate chips
Spoon mixture into baking pan (the size smaller than the 9x13). Put a piece of wax paper of pan. Using a heavy duty spatula, press down firmly all over the top. The key to keep these granola bars together is to press firmly.
Let stand for a few hours (if you can wait) Cut into bars.