Preheat oven to 350°F and line a muffin pan with cupcake liners.
In a medium bowl, stir together flour, cocoa powder, baking soda, baking powder, and salt. Set aside.
In a large bowl, cream the butter and sugar with a hand mixer or stand mixer until creamy.
Add the eggs, egg yolk, milk, and vanilla extract and cream together for another 2-3 minutes.
Add the flour mixture to the wet mixture and fold together with a silicone spatula until no large patches of dry flour remain. Don't overmix.
Spoon the batter into cupcake liners until about ¾ full.
Bake cupcakes for about 18 minutes or until a toothpick inserted comes out clean.
Let cupcakes cool completely. Using a small melon baller or knife, scoop out the middle section of each cupcake about halfway deep.
In a small saucepan, heat sugar on medium heat until melted and browned.
Remove pan from heat and pour in heavy cream while stirring constantly. Be careful as mixture will bubble up once you add the cream. Keep stirring until mixture is opaque light brown and coats the back of a spoon, about 2-3 minutes.
Stir in butter until melted and incorporated.
Transfer caramel to a small container to cool completely. It will thicken as it cools.
Spoon about 1-2 tablespoons into each cupcake until filled to the top.
In a small pot, bring about an inch of water to a simmer.
Add the egg whites and sugar to a heat-safe bowl that fits perfectly into the pot without touching the water.
Stir constantly until the sugar is completely dissolved, about 4 minutes. Rub a bit of egg white between your fingers and it should not feel grainy at all.
Remove the bowl from the pot and add the cream of tartar.
With a hand mixer or stand mixer, whisk the egg whites on low speed until frothy. Increase to high speed and beat until the meringue reaches stiff peaks, about 5-7 minutes. The meringue should stand up on its own when the whisk is pulled out of it.
Transfer meringue to a piping bag fitted with a large open star tip such as a Wilton #2D.
Starting from one side each cupcake, pipe in a side to side motion until you reach the other side and the surface of the cupcake is covered with meringue.
Using a blowtorch on a low setting, torch the meringue until browned and toasted. Sprinkle with a handful of crushed graham crackers.
Toasted cupcakes can be kept in an airtight container in the fridge for up to 3 days.