Line your 8-inch square pan with parchment paper, leaving some overhang on the sides for easy removal.
In a microwave-safe bowl, combine the peanut butter and honey. Microwave in 30-second bursts, stirring well after each, until the mixture is smooth, glossy, and fragrant—about 1 minute total.
Add the graham cracker crumbs to the melted mixture and stir until evenly coated and thickened—this will look crumbly but sticky enough to hold together.
Fold in the mini chocolate chips if using, distributing them throughout the mixture for bursts of chocolate in every bite.
Using a spatula or the back of a spoon, press the mixture firmly into the prepared pan, spreading it out evenly and smoothing the top. You should hear a slight crunch as you press down.
Place the pan in the refrigerator and chill for at least 2 hours, or until the mixture is firm and set. The bars will become dense and chewy as they cool.
Once chilled, lift the entire block out of the pan using the parchment overhang. Place on a cutting board and use a hot, sharp knife dipped in hot water to slice into squares or rectangles.
Serve immediately or store in an airtight container in the fridge for up to a week. For longer storage, wrap tightly and freeze for up to 3 months.