Line an 8×8 inch baking pan with parchment paper, leaving overhang on two sides for easy removal.

In a medium bowl, combine graham cracker crumbs, melted butter, sugar, and a pinch of salt. Mix until the texture resembles wet sand.

Press the crumb mixture firmly into the prepared pan, extending about halfway up the sides. Use the bottom of a glass to press evenly and compactly.

Refrigerate for 15 minutes to set the crust.

In a microwave-safe bowl, combine milk chocolate chips and coconut oil. Microwave in 30-second intervals, stirring between each, until fully melted and smooth.

Stir in vanilla extract.

Pour the melted chocolate over the chilled crust and spread into an even layer. Let it rest for 5 minutes until the chocolate is no longer runny but still soft.

Evenly sprinkle mini marshmallows over the chocolate layer, pressing them down gently so they stick but do not sink.

If desired, sprinkle with flaky sea salt for an extra pop of flavor.

Refrigerate the bars for at least 2 hours until completely set.

Use the parchment paper overhang to lift the bars out of the pan and cut into 16 squares with a sharp knife.