Line three baking sheets with parchment paper or silicone mats.
Sift together your powdered sugar, cocoa powder and almond flour, twice. Set aside.
Whisk together the egg whites and granulated sugar in a heatproof bowl over a double boiler. Whisk for about 2 minutes, until the sugar dissolves. You can tell it is ready when you pull the whisk up and touch the mixture with your fingers, you shouldn't feel any granules. Do not let the bowl touch the water or it will cook the eggs
Pour the mixture into the bowl of a stand mixer, fitted with the whisk attachment.
Whisk on low speed for 30 seconds, it should begin to foam. Increase the speed to medium for 2 minutes, until it becomes white and fluffy.
Increase the speed to medium-high, it should turn glossy and when you stop the mixer and pull the whisk out, you should have a stiff peak at the end of the whisk which only slightly bends at the end. This is how you know it is ready.
Pour in the powdered sugar/almond mixture
Gently fold them all together. Continue to fold and press the batter against the sides of the bowl. It is ready when it flows like lava from the rubber spatula, and you can make a figure 8 in the air without the batter breaking
Carefully transfer the batter into a piping bag with a medium circular tip.
Pipe out 70 macaron shells, piping at a 90 degree angle. Once they have all been piped out, bang each tray twice on your counter. Use a toothpick to pop any remaining air bubbles
Let them sit at room temperature for 30 minutes until they form a skin.
Preheat your oven to 325°F/162°C. Bake them one tray at a time for 15-17 minutes. Let them cool completely.
Decoration
Melt your dark chocolate and dip half of the shells into the chocolate. Sprinkle the hazelnuts over them.
Place the macarons in the fridge for 5 minutes so the chocolate will set and dry
Buttercream
Sift your powdered sugar and set aside.
In the bowl of an electric mixer with the whisk attachment, beat the butter until smooth - about 2-3 minutes
Add in the Nutella and salt and whisk together.
With the mixer running on low, slowly pour in the powdered sugar. Then add in the heavy cream. You may need to add more heavy cream depending on the consistency you want.
Increase the speed to medium and beat together for 1 minute.
Pour into a piping mag with a medium tip and pipe half of the macaron shells.
Notes
You will need to use a scale to make this recipe, it will make all the difference!
Crush the hazelnuts by placing them in a dish cloth and hitting them with a rolling pin.
Store the macarons in an airtight container in your fridge for up to 3 days.