In a medium saucepan over low heat, combine the heavy cream and chocolate chips. Stir continuously until melted and smooth. Once melted, remove from heat.
In a mixing bowl, whisk together the granulated sugar, eggs, and vanilla extract until combined. Slowly add the melted chocolate mixture to the egg mixture, stirring until completely incorporated.
Pour the chocolate filling into the pre-made graham cracker pie crust, smoothing the top with a spatula.
Bake the pie in the preheated oven for 25-30 minutes, until the filling is slightly set but still fudgy.
Remove the pie from the oven and evenly sprinkle the mini marshmallows on top of the pie. Return to the oven and broil for 1-2 minutes, keeping a close eye on it to avoid burning, until the marshmallows are golden brown.
Allow the pie to cool at room temperature for about 30 minutes. It will continue to firm up as it cools.
Once cooled, sprinkle crushed graham crackers on top and garnish with chocolate shavings.
Slice the pie into wedges and serve at room temperature or chilled.
Notes
Keep an eye on the marshmallows while broiling to prevent burning.