Preheat oven to 350F and grease and flour a 10"x15" sheet pan, line with parchment.
In a medium bowl, whisk flour, graham cracker crumbs, baking powder, and salt. Set aside
Using a stand mixer fitted with the paddle attachment, beat butter until smooth.
Add sugar and beat on med-high until pale and fluffy (2-3mins).
Reduce speed and add eggs one at a time, fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and buttermilk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition. Do not overmix.
Spread batter evenly into sheet pan pans. Smooth the top with a spatula.
Bake for approx. 15-18mins or until the cake is golden and springs back to the touch.
Cool in pan for 10mins then turn out onto wire rack to cool completely.
Cut out six 3.5" circles using a round cutter. Wrap individually in plastic and place in freezer.*
Ice Cream:
Grease six 1-cup ramekins and line with plastic wrap. Spread softened ice cream into each ramekin, fold over plastic wrap and freeze for at least 3 hours.
Meringue:
Place egg whites and sugar into the bowl of a stand mixer*, whisk until combined.
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is no longer grainy to the touch (approx. 3mins).
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)). Set aside.
Assembly:
Remove one cake circle from freezer, unwrap, and place on a small serving dish.
Remove one of the ice cream ramekins from the freezer and use your hands to warm up the bottom and sides. Pull out using the excess plastic wrap. Place on top of cake circle and press down. Return to freezer. Repeat with other 5 cakes and ice creams.
Remove one of the cakes from the freezer, dollop a generous cup of meringue on top and spread quickly over the top and sides.**
At this point you can either return them to the freezer until ready to serve or torch the meringue with a kitchen torch and serve immediately.
Alternatively, you can place them in a 500F oven for 1-2 minutes until meringue starts to brown.***
Notes
* You will have some cake scraps left over. I store these in an airtight container and snack on them, or you could use them to make cake pops. ** The ice cream will start to melt as soon as the meringue hits it, so be sure to do this quickly! Also make sure your meringue is completely cool. *** If baking in the oven, ensure meringue completely covers all of the ice cream and cake. It needs to insulate the ice cream so make sure there are no gaps.