Prepare the Pan: Grease a 9x13-inch baking pan with butter or non-stick cooking spray.
Melt Butter and Marshmallows: In a large pot, melt the butter over medium heat. Add 7 cups of mini marshmallows to the melted butter and stir continuously until fully melted and smooth.
Add Vanilla Extract: Remove the pot from heat and stir in the vanilla extract.
Combine with Golden Grahams: Add and gently fold in the Golden Grahams cereal until evenly coated with the marshmallow mixture. Toss in 1 cup of the reserved mini marshmallow and mix in.
Press into Pan: Transfer the mixture to the prepared baking pan. Press down gently with a spatula to spread it evenly. Be careful not to press too hard, as you want to keep the mixture light and airy.
Add Remaining Marshmallows and Hershey’s Bars: Evenly spread the remaining 1 cup of mini marshmallows and Hershey Bars pieces all over the top of the golden grahams.
Cool and Set: Allow the bars to cool at room temperature for about 1 hour, or until set. For quicker setting, you can place the pan in the refrigerator for about 20-30 minutes.
Cut and Serve: Once set, cut the mixture into bars of your desired size.