Line a 8x8 inch pan with parchment paper and set aside.
Combine 1/2 cup peanut butter and 1/3 cup honey in a medium size sauce pan. Cook on low for 2 - 3 minutes, stirring occasionally. Remove from heat and stir in vanilla.
Add in the 3 cups dry cereal and stir until completely coated. It it seems a little sticky, add an additional 1/2 - 1 cup. Press into the lined pan. Use a piece of parchment paper to press firmly down on the bars.
Refrigerate bars for one hour, or until ready to serve.
Notes
These cereal bars are best kept chilled in the refrigerator to keep shape.