line a muffin pan with 8-10 muffin liners. preheat the oven to 250F
add egg whites to a clean mixing bowl. whisk on high until the egg whites get foamy. on medium-high, add sugar a teaspoon at a time every 10-15 seconds. after adding about 1/4 c of the sugar, add the white vinegar and salt. add the remaining sugar one teaspoon at a time until all the sugar has been added. adjust speed to high and beat until add the sugar has dissolved. test by rubbing meringue between your fingers. once you no longer feel sugar, its ready. melt the chocolate over a double boiler or in a microwave safe bowl in 30 second intervals, stirring unti all the chocolate has melted.
using a spoon, drop a swirl of melted chocolate on top of the meringue. using a large spoon, scoop a generous amount of meringue onto the spoon. gently drop meringue into a muffin liner, using the second spoon to help scrape the meringue into the cup. repeat with the remaining liners until all the meringue is gone. add melted chocolate to the bowl of meringue as needed. if you want more chocolate swirl on the top of each individual meringue, swirl an additonal teaspoon on top of each meringue, using a toothpick to help create the swirl.
place meringues into the oven for 90 minutes. at the end of the time, turn the oven off, crack the door and leave in the oven for 2-4 hours. remove from the oven, gently crack open the middle of the meringues, fill with rosè berries and whipped cream.