For the Hoosier mama s'more pie: Combine 3/4 cup (178mL or 181g) of the milk and 1/2 cup (119mL or 116g) of the cream in a small, heavy saucepan. Bring to a boil over medium-high heat, stirring occasionally so the milk does not scorch on the bottom of the pan.
Meanwhile, whisk the remaining 1/4 cup (59mL or 60g) of the milk into the cornstarch to make a slurry. Set aside.
Place the egg into a medium, deep heatproof bowl. Whisk in the sugar until well combined. Slowly pour in the slurry and whisk until smooth. Gradually whisk in the hot milk mixture, stirring until well combined.
Pour the mixture back into the saucepan and cook over medium heat, whisking constantly, until it starts to thicken and just begins to boil. Whisk at a boil for 2 more minutes. Remove the saucepan from the heat and add the chocolate and butter. Whisk until both are melted and well incorporated. Whisk in the vanilla paste and salt.
Pour the pastry cream through a fine-mesh strainer into a heatproof bowl. Place a piece of plastic wrap directly onto the surface of the pastry cream and gently smooth with your fingers. This will prevent a skin from forming on the top of the pastry cream. Chill in the refrigerator until it is firm, about 2 hours. You can speed this process by placing the bowl of pastry cream over an ice-water bath.
For the chocolate ganache: Place the bittersweet chocolate in a small, heatproof bowl. Bring the cream to a boil over medium heat. Pour the cream over the chocolate. Let stand for 30 seconds. Wisk the cream and chocolate until smooth.
Spread the ganache in the graham cracker crumb crust shell and place the shell in the refrigerator until the ganache is set, about 30 minutes.
Remove the chocolate pastry cream from the refrigerator and transfer to the bowl of a stand mixer fitted with the whisk attachment. Whip on Medium until it is light and fluffy. Remove from the stand mixer and set aside. Thoroughly wash the stand mixer bowl.
In the bowl of the stand mixer still fitted with the whisk attachment, whip the remaining 1/2 cup (119mL or 116g) of the cream to soft peaks. Gently fold the whipped cream into the pastry cream.
Remove the prepared pie shell from the refrigerator. Spoon the pastry cream into the shell, over the ganache. Gently smooth the top of the pie with an offset spatula, making sure the pastry cream touches the edge of the pie shell. Chill in the refrigerator until the pastry cream is set, about 1 hour.
For the creamy meringue: Fill a 1-quart (948-mL) saucepan halfway with water and bring to a simmer over medium-high heat.
Combine the egg whites and granulated sugar in a medium stainless steel bowl and whisk to incorporate the sugar and break up the whites. Rest the bowl on top of the pot of simmering water and whisk constantly, until the egg whites reach 165 degrees F on an instant-read thermometer.
Pour into the bowl of a stand mixer and whip on high until the mixture is lukewarm.
Pour it directly onto the center of the pie and, with the back of a serving spoon, spread it out from the center in concentric circles. Toast with a butane torch. Be sure to get a few spots "extra toasty," as if it got scorched in the campfire! The finished pie can be served immediately.
Propane gas torches are highly flammable and should be kept away from heat, open flame, and prolonged exposure to sunlight. They should only be used in well-ventilated areas. When lighting a propane gas torch, place the torch on a flat, steady surface, facing away from you. Light the match or lighter and then open the gas valve. Light the gas jet, and blow out the match. Always turn off the burner valve to "finger tight" when finished using the torch. Children should never use a propane gas torch without adult supervision.