Preheat oven to 350F. Line a 6 inch cake pan with parchment paper and grease the sides of the pan

In a medium bowl, add the graham cracker crumbs, melted butter and salt. Mix with a spoon until it looks like wet sand. Pour this sandy mixture into the 6-inch pan and press down firmly with your hand OR the back of a measuring cup. Bake the graham crust for just 10 minutes and remove from oven

In a large bowl, add the flour, cocoa powder, baking soda, espresso powder, and salt. Whisk to combine.

In a separate medium bowl, whisk the oil, sugar, egg, vanilla extract, and buttermilk together. Pour the wet ingredients into the flour mixture and whisk until smooth and thoroughly combined.

Pour the cake batter into the prepared 6-inch cake pan with the baked and cooled graham crust

Bake for 25–30 minutes or until the cake is baked through- cake should be puffed and completely set. To test for doneness, insert a toothpick or a knife into the center of the cake. If it comes out clean, it’s done

Make sure to allow the cake to cool completely before pouring the mousse on top

Once cooled, place a 6-inch cake ring outside the cake. Line the outside of the cake with a strip of acetate, tucking it inside of the cake ring. Tape the top of the acetate to ensure there are no gaps at the seam

In a small bowl, sprinkle gelatin over 1 tablespoon cold water. Let sit for at least 4 minutes until set. This is "blooming" the gelatin.

Set up a double boiler- Place a medium saucepan filled with water over medium heat until water comes to a simmer. Place a heat proof bowl on top of the medium saucepan with simmering water- NOT IN THE BOWL. It should rest on top. Melt semisweet chocolate and butter, stirring occasionally, until smooth. Add gelatin mixture, stirring until dissolved.

Remove from chocolate mixture from the heat and add in the egg yolks. Whisk whisk until well combined. Let this mixture cool until it is room temperature

In a large bowl, add egg whites and salt. Whisk (you can also use a hand-mixer) until stiff peaks form

Using a nonstick spatula, fold the egg white mixture to the chocolate mixture in 3 parts, being as gentle as possible. Next, gently fold in whipped cream

Pour over the cooled cake layer (this should be lined with the acetate at this point) and let set in the fridge

Using stand-mixer with the whisk attachment beat the egg whites and sugar on medium-high until stiff peaks form. It should look smooth and glossy

Spoon the meringue on top of the set mousse inside the acetate strip

Let a set in the refrigerator at least 4 hours

Remove from the refrigerator and remove acetate strip

Torch the outside of the meringue, making sure not to touch the mousse because it will melt

Cut into slice and serve!