With the mixer running on low speed, slowly add the milk mixture. Increase the speed to medium and beat until combined, 20 to 30 seconds. Slowly pour the hot coffee into the batter and mix until just combined. Using a spatula, give the batter a couple of turns to make sure it is fully mixed.

Divide the batter evenly between the prepared pans. Bake for 25 to 35 minutes, until a wooden skewer or toothpick comes out with the tiniest bit of crumb.

Transfer the cakes to a wire rack and let cool for 30 minutes. Turn the cakes out onto the rack, remove the parchment paper, and let cool completely. Once cool, the cakes can be frosted or wrapped in plastic wrap and refrigerated overnight.

In a medium, heavy-bottomed saucepan fitted with a candy thermometer, combine the corn syrup, sugar, room-temperature water, and salt. Bring to a boil over medium-high heat, until the temperature reaches 240 [120C]; this will take a few minutes. Immediately remove the saucepan from the heat, and whisk in the gelatin. Set aside while whisking the egg whites.

Turn the stand mixer to low speed, and carefully pour the hot sugar syrup along the side of the mixing bowl, being careful not to hit the whisk attachment as your pour (transferring the hot mixture to a liquid measuring cup with a pour spout might make this task easier). When all the syrup is in the bowl, turn up the speed to medium-high and continue whisking until the mixture has doubled in volume, is quite thick and glossy, and sides of the bowl have cooled, 8 to 10 minutes. Add the vanilla and mix until combined.

Whisk together the graham cracker crumbs and sugar in a medium bowl. Add the melted butter and mix with a spatula until evenly incorporated. Spread the mixture on the prepared pan and toast in the oven until golden brown, 5 to 6 minutes.