In a medium bowl, mix together crushed graham crackers, melted butter, and brown sugar until it resembles wet sand and holds together loosely when squeezed.
Dump the graham crust mixture into a 6" fluted deep tart pan. Press the graham crumbs down and into the sides of the tart pan until it's tightly packed. Let the graham crust chill in the fridge while you prepare the filling.
Chocolate Ganache Filling
Put the chopped chocolate in a bowl and set aside.
In a small pot, heat the heavy cream until it just begins to simmer. Pour the cream over the chocolate and let it sit for 2 minutes.
After 2 minutes, slowly start stirring the mixture until all the chocolate has melted and the ganache becomes thick and smooth. Let it cool to room temperature.
Once cooled, pour the ganache into the tart pan lined with the graham crust. Smooth over the surface of the ganache with an offset spatula, if needed. Refrigerate tart for at least 2 hours or until the ganache has set.
In a small pot, bring about an inch of water to a simmer.
Add the egg whites and sugar to a heat-safe bowl that fits perfectly into the pot without touching the water. When the water comes to a simmer, place the bowl on top of the pot.
Stir constantly until the sugar has completely dissolved, about 4 minutes. Rub a bit of egg white between your fingers and it should not feel grainy at all.
Remove the bowl from the pot and add the cream of tartar and vanilla extract.
With a hand mixer or stand mixer, whisk the egg whites on low speed until frothy. Increase to high speed and beat until the meringue reaches stiff peaks, about 5-7 minutes. The meringue should stand up on its own when the whisk is pulled out of it.
Transfer meringue to a piping bag fitted with a large open star tip such as a Wilton #2D. Holding the piping bag vertically, pipe small "kisses" on top of the ganache, starting from the outside and working towards the middle of the tart.
Using a blowtorch on a low setting, torch the meringue until browned and toasted. If any of the ganache filling has melted from the heat of the torch, return the tart to the fridge until ready to serve.