Preheat oven to 350°F. Lightly grease a 9-inch pie pan if needed.
In a bowl, mix graham cracker crumbs, melted butter, and sugar until evenly combined. Press firmly into the bottom and sides of the pie pan to form a compact crust. Bake for 8 minutes, then remove and let cool completely.
In a heat-safe bowl, melt chocolate chips and butter together in short intervals, stirring each time, until smooth and fully melted. Allow the mixture to cool slightly.
Stir sugar into the melted chocolate mixture until fully incorporated. Add eggs one at a time, mixing gently after each addition to create a smooth batter. Stir in vanilla extract.
Add flour and salt to the mixture. Fold gently until just combined, being careful not to overmix.
Pour the batter into the cooled crust. Spread evenly with a spatula to ensure a level surface.
Bake for 20 to 25 minutes, or until the edges are set and the center remains slightly soft.
Remove from oven and immediately sprinkle mini marshmallows evenly over the top. Return to oven and bake for an additional 3 to 5 minutes until marshmallows are puffed and lightly golden.
Remove from oven and allow the pie to cool before slicing. This helps the filling set while staying gooey inside.