Heat heavy cream in a small saucepan over medium heat until it just begins to simmer.

Pour hot cream over chocolate chips in a heatproof bowl, let sit for 2 minutes, then stir until smooth.

Stir in butter and vanilla until fully incorporated, then pour ganache into the graham cracker crust.

Refrigerate for at least 3 hours until the filling is firm.

When ready to serve, scatter mini marshmallows over the top in an even layer.

Broil on high for 1 to 2 minutes until marshmallows are golden, watching constantly, then slice and serve immediately.