In a food processor, grind together the powdered sugar with the almond powder and cocoa so there are no lumps. Using a standing electric mixer and at slow-medium speeds, beat the egg whites until they begin to rise and hold their shape. While whipping, gradually beat in the granulated sugar until very stiff and firm.
Carefully fold the dry ingredients, in two batches, into the beaten egg whites with a flexible rubber spatula. When the mixture is just smooth and there are no streaks of egg white, stop folding and scrape the batter into the pastry bag.
Pipe the batter on the parchment-lined baking sheets in 1/2-inch circles. Tap the baking sheet a few times firmly on the counter top to flatten the meringues, then bake them for 15 minutes. Let cool completely then remove from baking sheet.
To assemble, you match up similar sized meringues. Depending on size of meringues, spread 1/2 – 1 teaspoon of nutella on one cookie’s inside and fluff on the other side, and then gently press the matching cookie on top, forming a sandwich.
You can store in an airtight container or in the fridge for at least one day before serving and the meringues can keep up to 5 days, after that they may be stored in the freezer up to 3 months!