Sift together the powdered sugar, almond meal and 2 tablespoons of espresso so there are no lumps (usually i just use a fork to break any large lumps). if your almond meal isn't so fine, you can put the ingredients into a blender or food processor to make it finer. personally, i'd just use the sifter and dump out any remaining crumbs that didn't make it through the sifting process.
In the bowl of a standing electric mixer (or if you prefer, you can use a bowl and hand mixer), beat the egg whites until they begin to rise and hold their shape. while whipping, beat in the granulated sugar until very stiff and firm, about 2 minutes.
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 (standing the bag in a tall glass helps if you’re alone).
Pipe the batter on the parchment-lined baking sheets in 1.35-inch (3.5 cm) circles evenly spaced one-inch (3 cm) apart. quickly after it's piped, sprinkle a few espresso powder over each shell (this step is optional, personally i do it because i like how the macarons look once they're baked).
Rap the baking sheet a few times firmly on the counter top to flatten the macarons. then it let sit for at least 30-60 minutes depending on humidity (okay, i've done it with just 15 minutes before and they turned out fine, but whatever you do, do not skip this step; even at just 15 minutes) before baking them in the oven, 15-17 minutes. let cool completely then remove from baking sheet.
Make sure to pair up all the cookie shells so they are as close as possible in size. then using a knife, spread a good amount of nutella on the inside of the macarons then sandwich them together. (you can pipe the filling it if you prefer less mess. i personally sometimes can't be bother to go through the hassle of putting my filling in a bag and cleaning up after it.)
Let them stand at least one day (keep them refrigerated) before serving (serve at room temperature), to meld the flavors. or if you can't wait to dig in and eat, i say wait a few hours, at least! (shhhh, i've eaten them newly assembled too, and they taste just as yummy. just a little crunchy, but that's okay. hehehe). but really, for the best optimal flavor and taste, you must wait at least one day. they really are that good and worth the wait!