Pulse graham crackers in a food processor until fine crumbs form (or crush using a plastic zip top bag and rolling pin/can).

Add brown sugar, salt and melted butter to the bowl and pulse until combined.

Press into a 14-inch rectangle tart pan (see notes for other pan sizes). Use the bottom of a cup to press the crumbs tightly into the bottom and sides of the pan.

Finely chop chocolate and place into a heatproof bowl.

Heat the heavy cream in a small saucepan over medium heat until bubbles form at the edges of the pan.

Pour the hot cream over the chocolate and let sit for 2 minutes.

Stir the cream and chocolate until smooth.

Combine egg whites, sugar and cream of tartar in a heat proof bowl set over a pot of gently simmering water (I used the stand mixer bowl to reduce amount of bowls needed).

Heat the mixture, while stirring constantly, until an instant thermometer reads 160 degrees, about 5 minutes.

Remove the bowl from the heat and using the whisk attachment of your stand mixer, mix on high speed until stiff, shiny peaks form, about 5 min. Mix in the vanilla.