Pulse graham crackers in a food processor until fine crumbs form. If you don’t have a food processor on hand, place the crackers in a Ziplock bag and smash the crackers with a cup until fine crumbs form.
Into a small to medium mixing bowl, add the graham crackers crumbs, and melted butter. Mix with a spoon until the crumbs are coated with butter.
Transfer the crumbs into a prepared 9 by 9 inch pan, pressing evenly and firmly into the pan.
Bake the crust in a 180c (350f) preheated oven for 8 minutes. Keep an eye on the crust and make sure it doesn’t burn. Take the crust out of the oven and let it cool to room temperature.
For the brownie batter
In a large mixing bowl, add the butter and the dark chocolate. Melt completely in the microwave or on a bain Marie. Mix with a whisk until silky and smooth.
Add the granulated sugar, espresso powder, vanilla extract, and kosher salt, sift the cocoa powder, and mix with a whisk until well combined.
Add the eggs and egg yolk and mix until well combined and smooth.
Sift the flour and fold the mixture with a rubber spatula until the batter is just combined. Do not overmix.
Pour the batter onto the graham cracker crust. Bake in a 180c (350f) preheated oven for 30-35 minutes. Do not overbake it to keep it fudgy!
Make the Swiss meringue
Start by combining egg whites and sugar in a heatproof bowl. Place the bowl over a pot of simmering water, creating a double boiler.
Whisk the mixture constantly while heating until it reaches 160°F (71°C) or feels smooth and not grainy when rubbed between your fingers.
Once the desired temperature is reached, remove the bowl from heat and transfer the mixture to a stand mixer fitted with a whisk attachment.
Beat on high speed for about 5-7 minutes, or until stiff, glossy peaks form and the meringue has cooled to room temperature.
Top the completely cooled brownies with the meringue and make swirls using an offset spatula.
Use a kitchen torch to slightly burn the top of the meringue to create a toasty look and give it a toasty flavor. Serve and enjoy.
Notes
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.
Don’t overmix the batter. For a fudgy texture, avoid overmixing your brownie batter once you add flour. Mix just until combined to keep from incorporating too much air.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Monitor baking time. Keep an eye on your brownies as they bake. overbaking can lead to dry brownies instead of that desired fudgy consistency. A toothpick inserted should come out with a few moist crumbs.
Cool completely before topping. Allow your brownies to cool completely before adding the Swiss meringue topping to prevent melting or sliding off due to residual heat.
Torch carefully. Use a kitchen torch on low heat setting to gently toast the Swiss meringue without burning it, moving in small circles until you achieve an even golden-brown color.
Serve freshly torched. For best results, serve your brownies shortly after torching so that everyone can enjoy that freshly-toasted marshmallow flavor and texture.
Line your baking pan with parchment paper to prevent the brownies from sticking to the pan.