Prepare the Base

1. Mix the Graham Cracker Crumbs: In a medium-sized bowl, combine the graham cracker crumbs and sugar.
2. Add Butter and Vanilla: Pour in the melted butter and vanilla extract, and stir until everything is well combined. The mixture should feel slightly wet but crumbly.
3. Press Into the Pan: Transfer the graham cracker mixture into an 8×8-inch baking dish (lined with parchment paper for easy removal). Press the mixture firmly into the bottom to form an even base. You can use the back of a spoon or your hands to do this.
4. Chill: Place the pan in the fridge for 15-20 minutes to allow the base to set before adding the next layer.

Make the Chocolate Layer

1. Melt the Chocolate: In a microwave-safe bowl, combine the semi-sweet chocolate chips and heavy cream. Microwave in 20-30 second intervals, stirring in between, until the chocolate is smooth and fully melted.
2. Pour the Chocolate: Once melted, pour the chocolate over the graham cracker base. Use a spatula to spread it evenly, covering the entire surface.
3. Chill Again: Place the pan back in the fridge for 15-20 minutes, or until the chocolate layer has firmed up slightly.

Add the Marshmallows

1. Top with Marshmallows: Once the chocolate layer has set, remove the pan from the fridge. Sprinkle the mini marshmallows evenly over the chocolate layer.
2. Press Down Gently: Press the marshmallows into the chocolate layer slightly so they don’t just sit on top. This will help them stay in place when you slice the squares later.
3. Final Chill: Put the pan back into the fridge for at least 45 minutes or until the squares are firm enough to cut.