Preheat oven to 100˚ C. In a heatproof bowl combine the egg whites, sugar and cream of tartar. Fill a medium pot with hot water and heat to a medium boil over medium heat. Place the heatproof bowl on top of the pot and whisk with a hand mixer until the mixture is silky with high peaks and warm to the touch. Take the bowl off the heat and mix further until the mixture is completely cool. Spread the mixture into two even circles on a baking paper lined baking sheet. Alternatively make individual meringues by making smaller circles on the lined baking sheet. Swirl the cocoa powder through the meringue, careful not to mix too much. Bake for 90 minutes and then turn the oven off to cool with the meringues inside for another 30-60 minutes. Whisk the cream till stiff peaks form. Place the first meringue on a serving plate or cake stand. Top the first meringue with cream, cherries, pistachios and chocolate shavings. Place the second layer on top and repeat with cream, cherries, pistachios and chocolate shavings.