Preheat oven to 325. Butter and line an 8 or 9" round pan with parchment paper.

Whisk in the sugar, salt and vanilla.

Add the eggs and whisk until smooth. Add the cocoa and mix.

Pour batter into prepared pie pan and bake for 18 minutes.

When you have about 10 minutes left on the baking time for the cake, begin whipping the egg whites in a stand mixer or with a hand mixer. When whites are frothy, add the sugar in a slow and steady stream.

Turn mixer to high, add the salt and vanilla. Let it whisk until thick and glossy and you have stiff peaks, toward the end add the vinegar and cornstarch.

Melt the chocolate in the microwave in 30 second increments, stirring between every 30 seconds. While the chocolate is still melty but cool, pour it into one side of the meringue, with a spatula, fold it in in 3-4 big folds, leaving big streaks of chocolate.

Remove the cake from the oven and raise oven temperature to 350 F.

Gently dollop the meringue onto the cake. If you need to spread it a bit, do so very cautiously so as not to overmix the chocolate. Return cake to oven and bake for another 20 minutes.

Let cool and serve at room temperature.