Preheat oven to 325°F. Grease the sides of a 9” tart pan with nonstick cooking spray, then line the bottom with parchment paper. If you don’t have a tart pan you can use a 9” pie pan and spray that with nonstick cooking spray. Set aside.
In a medium sized bowl stir the graham cracker crumbs, sugar, and melted butter together until combined.
Pour the graham cracker mixture into the tart or pie pan. Press it firmly in the bottom of the pan and up the sides into an even layer.
Bake for 8 minutes. Remove from oven and let cool completely. If doing a no-bake recipe, rather than bake the crust, place the pie pan in the refrigerator to chill for 30 minutes (or in the freezer for 15 minutes) while you prepare the pie filling.
Make the chocolate pudding layer
In a small saucepan over medium heat whisk the sugar, milk, cornstarch, and unsweetened cocoa powder. Bring the mixture to a simmer, whisking frequently.
Meanwhile add the 3 egg yolks to a small/medium size bowl. Use a fork or whisk to break up the egg yolks.
Once the chocolate mixture is simmering, dip a liquid measuring cup into the mixture scooping out about ¼ cups worth (doesn’t have to be exact!). Now we temper the eggs: slowly drizzle the hot liquid into the egg yolks, whisking as you do so. Now pour the tempered eggs yolks into the saucepan and whisk constantly until the mixture comes to a gentle boil. Once big bubbles break the surface, remove from heat and use a heat proof rubber spatula to stir in the butter, chopped chocolate and vanilla extract.
Once the chocolate mixture is smooth, pour it into the pie crust. Spread into an even layer then cover with plastic wrap, making sure the plastic touches the surface of the chocolate to prevent a film from forming. Chill in the fridge for 4 hours or overnight.
Make the marshmallow cream
In a small saucepan set over medium heat add the granulated sugar, corn syrup, water, and pinch of salt. Boil, stirring occasionally until the mixture reaches 240°F on a candy thermometer. (It will take around 8 minutes or so to reach 240°F… you will need to use a candy thermometer for this though)!
While the sugar mixture is boiling add the egg whites and cream of tartar to a stand mixer bowl fitted with a whisk attachment. Whip on medium-high speed until soft peaks form.
Once the sugar reaches 240°F remove from heat, and turn the mixer speed to low (that has the egg whites in it) and carefully and slowly drizzle the syrup mixture down the side of the mixer bowl and into the egg whites. Once all of the syrup has been added turn the mixer to medium-high speed and whip for 7-10 minutes or until stiff glossy peaks form. During the last minute of beating, add the vanilla extract.
Spoon the marshmallow cream on top of the chocolate layer. Swirl into an even layer. Right before serving use a kitchen torch to torch the marshmallow cream. If you don’t have a kitchen torch, preheat your oven to broil. Broil for 1-2 minutes, until the marshmallow is toasted to your liking.
To serve, oil a chef’s knife, slice, and serve! Store leftovers covered in the refrigerator for up to 4 days.