Option 1, Swiss method (best for brown sugar meringue): set a pot filled a little less than halfway with water over medium low heat and bring the water to a simmer. Set a bowl over the pot (it shouldn't touch the water) and add the sugar then the egg whites to the bowl and quickly whisk well. Keep stirring, use a rubber spatula to scrape the sides of the bowl, as the mixture heats. Lift the spatula and pinch some of the dropping liquid, if you cannot detect any sugar granules then it's done warming. Pour it into the bowl of a stand mixer and affix the whisk attachment, start whisking on low then work up to medium (speed 6). Whip until you have stiff peaks, adding the salt and vanilla toward the end.
Option 2, French method: In the bowl of a stand mixer fitted with the whisk attachment, begin whipping the egg whites slowly, and once frothy, slowly pour in the sugar- very slowly to let the granules dissolve before adding too much at once. Once the sugar is all in, add the vanilla and salt. Whip until stiff peaks; when you can turn the whisk upside down and it holds shape.
Dollop the meringue over the ganache then place in the fridge to chill. After about 30 minutes, torch the top with a kitchen torch.
For clean slices, warm a knife under hot water then dry it and slice. Store leftovers in the fridge.