Set oven rack to the middle position. Preheat oven to 212F/ 100C degrees. Line one large baking sheet with parchment or a silpat. (Or two smaller cookie sheets.)

Dampen a paper towel with a little apple cider or white vinegar and wipe the inside of the bowl of a stand mixer or a large bowl. Do the same to the whisk attachment(s.) (This ensures there's no grease or fat on the utensils.)

Add the egg whites to the mixing bowl and begin to whip with the whisk attachment on medium-low speed until the egg whites are foamy.

Gradually add the sugar 1 tablespoon at a time, waiting about 15 seconds between each addition.

Once all of the sugar has been added, add the salt and vanilla and continue to beat about 5-10 minutes more until very stiff glossy peaks form. Be sure to check for graininess using your index finger and thumb to smoosh together a tiny bit of meringue. If you can still feel many sugar granules, keep mixing a bit longer. Then, when done, drizzle about half of the Nutella directly over the top of the meringue. Don't mix this in. (If needed pop the Nutella into the microwave for a few seconds so it's a consistency you can drizzle.)

Then using a cookie scoop (my preferred way,) or a spoon, dollop about a ping-pong-sized drop of meringue onto the prepared sheets, leaving about 2 inches between each cookie. Use up about 2/3rds of the meringue in this step.

Then using a small spoon, place a small drop of Nutella onto the center of each cookie, then drizzle the rest of the Nutella over the other 1/3 of the meringue in the bowl. Using the same spoon you scooped the cookies with, add another (smaller) dollop of meringue over the little mounds of Nutella. (So, meringue, Nutella, meringue)

Use a small offset spatula or butter knife to gently shape the meringues into rounds if desired and if they are too tall. You can use the pictures for reference. They are still very rustic, but not too tall they are difficult to bite into.) Top each meringue with a sprinkling of sea salt.

Place the cookie tray(s) into the pre-heated oven and bake for about 55-60 minutes, rotating the pan halfway through baking. The cookies are done when they are dry and can easily be pulled off paper. ( Make sure the bottoms are very very dry and not sticking) At this point, turn the oven off and leave the cookies in the closed oven for 30 minutes to dry completely.

Store the baked meringues in an airtight container at room temperature, free from moisture.