4 large egg whites, room temperature
1/8 tsp. cream of tartar
1/8 tsp. table salt
1 cup plus 2 Tbs. granulated sugar
1 ½ tsp. cornstarch
1 Tbs. red wine vinegar
¼ cup unsweetened Dutch-processed cocoa powder
1 cup heavy whipping cream
Zest of 1 tangerine (approx. 1 ½ tsp.)
1 ½ cups of fresh berries (we used raspberries, blue berries, and black berries)
Position a rack in the center of the oven and preheat oven to 350 degrees F. Cut a piece of parchment paper so that it fits flat on a baking sheet. With a pencil, trace a circle around a 9-inch cake or pie pan in the center of the parchment. Line the baking sheet with the parchment, pencil side facing down, still allowing you to see the circle.
Using an electric mixer with a whisk attachment, whip the egg whites, cream of tartar, and salt in a large dry bowl on medium speed until foamy, about 30 seconds. Gradually add 1 cup of the sugar and then the cornstarch and vinegar; whip on medium high until the whites hold stiff peaks and look very glossy, another 3-5 minutes. Add the cocoa powder and mix on low speed until mostly combined, 20-30 seconds, scraping the bowl as needed. Finish mixing the cocoa into the meringue by hand with a rubber spatula until well combined and no streaks of white remain.
Pile the prepared meringue inside the circle on the parchment paper. Using the spatula, spread the meringue to even it out slightly – it doesn’t need to align perfectly with the circle, and it shouldn’t be perfectly smooth or overworked. (The natural swirls and ridges give the finished meringue character!)
Bake for 10 minutes, then reduce the oven temperature to 300 degrees F. and bake until the meringue has puffed and cracked around it’s edges, another 45-50 minutes. Turn off the oven, prop the oven door open, and leave the meringue in the oven to cool to room temperature, at least 30 minutes. (This allows the meringue time to cool gradually, and it won’t collapse as much.)
Just before serving, place the meringue onto a serving platter. In a chilled bowl, beat the cream with the remaining 2 Tbs. sugar until it holds soft peaks. Whip in the tangerine zest, making sure it’s evenly distributed. Pile the prepared whipped cream onto the meringue, spreading it almost out to the edge, and then top with the berries. Slice into wedges with a serrated knife.