Line an 8x8 or 9x9 inch square pan with parchment paper, leaving about 2 inches of overhang on each side.

In a large bowl, combine the oats and Rice Krispies. Set aside.

In a medium-sized sauce pan combine the peanut butter, brown sugar, honey and butter over medium-low heat. Allow the mixture to melt while stirring - it should come to a very slow boil and the sugar should dissolve. Continue stirring slowly while the mixture boils for 2 to 3 minutes.

Pour the peanut butter mixture into bowl with the oats and Rice Krispies and stir to combine. Once the oats and Rice Krispies are fully coated, press the mixture into the prepared pan until tightly packed. Sprinkle the Reese's Pieces on top and press them in firmly.

Allow the bars to harden in the freezer for about 15-30 minutes or in the fridge for 1 hour. Once hardened, cut into bars.