Preheat your oven to 300°F. Line 2 baking sheets with parchment paper.
Put the egg whites and a pinch of salt in the bowl of a stand mixer. Start off slowly and beat the egg whites until they form bubbles all around the same size, about 2-3 minutes. Gradually increase the speed of the mixture and very slowly add the sugar. Add the vinegar or lemon juice. Beat for another 4-5 minutes. The egg whites will be very glossy and will hold their peaks when you lift them from the bowl with the whisk.
Put the meringue into a piping bag with a star or large round tip and pipe out mixture onto the baking sheets in cookie-sized dollops. You could also skip the piping bag and use two small spoons.
Put the sheets into the oven, close the door, and turn the oven off. Let the cookies stay in the oven overnight. They will harden and dry out. If you are not going to use them right away, put them in an airtight container for up to 1 week.
To Make The Eton Mess:
Start with a few meringues and break them apart. Put them in the bottom of the serving bowl or jar. Layer some berries on top.
Add a layer of whipped cream and raspberry sauce.
Keep layering until you run out of the components. Serve immediately.