Make sure your stand mixer bowl is super clean. Whisk eggs whites on low speed for 2 minutes. Increase speed to low-medium and add vinegar and whisk for 3 more minutes. Increase speed to medium high and add 1 teaspoon vanilla and the salt. Whisk until soft peaks form. Slowly add sugar (or Truvia) and continue to whisk on high until you see stiff glossy peaks and the sugar is dissolved.
While the eggs are beating, DO NOT grease your springform pan*. But DO cut a piece of parchment paper to fit on the bottom.
Bake for 90 minutes. DO NOT OPEN THE DOOR after you put it in. At the end of the baking time, turn the oven off and keep the door shut for at least 2 hours.*
*Did I mention, NOT to open the door once you start baking? And NOT to open the door for at least 2 hours after you turn off the oven? Ok, just checking. This is what keeps the top from falling. Otherwise, you can’t do the whole layering thing. Keeping the crispy top crust separate from the foam cushiony base lets you experience all the layers in their full expression. And come on, crispy sweet crunchy stuff is fun to eat.
*Do Not grease the parchment paper or springform pan. I did this and ended up with a jelly-like oil slick that was super disgusting. I still have nightmares. Ick.