Make the macarons:

1. In a large mixing bowl, use a fine-mesh sieve to sift the almond flour, confectioners' sugar, and cocoa powder together. Pressing down on any clumps, and set aside.
2. Use a hand mixer or stand mixer with the whisk attachment on medium speed to beat the egg whites until they become foamy and soft peaks form, about 2 minutes. Turn the mixer up to high speed and gradually add in the granulated sugar. Beat until stiff, glossy peaks form, about 2 more minutes.
3. Using a spatula or wooden spoon, gently fold half of the dry ingredients into the egg white mixture. Fold in the remaining half of the dry ingredients. Keep folding gently until it reaches a flowing lava-like consistency. Do not overmix.
4. Line a large half sheet baking pan with parchment paper or a silicone baking mat (a macaron silicone mat will make it really easy to measure out the macaron shells).
5. Spoon the mixture into a piping bag fitted with a 1/2 inch round tip. Pipe 1-inch rounds on the lined baking sheet, spacing them about an inch apart.
6. Tap the baking sheet firmly against the counter 3-4 times to release any air bubbles from the macarons. Any remaining bubbles can be popped with a toothpick. Allow the macarons to sit at room temperature for 25-30 minutes to rest and form a skin.
7. Meanwhile, preheat the oven to 300F degrees.
8. Place the baking tray in the center rack of the oven and bake for 14-15 minutes. Let the macarons cool on the baking sheet for 5 minutes before carefully transferring them to a cooling rack to cool completely. Cooled macaron shells should be easy to peel off the parchment paper. 

Make the chocolate buttercream:

1. Melt the chocolate either on the stove or in the microwave:
   • On the stove: Bring 2 inches of water to a low simmer in a saucepan over medium-low heat. Then turn the heat to low and place a large heatproof bowl of chocolate chips with vegetable oil on the mouth of the pot. Make sure that there is a gap of a few inches in between the bottom of the bowl and the water (You can also place a bowl on a steamer attachment on top of your pot). Stir the chocolate constantly as it melts. Stir until the chocolate is completely smooth and melted. This should take a few minutes. 
   • In the microwave: The second way to melt chocolate (and an easier way) is in the microwave. Place the chocolate and vegetable oil into a microwave safe bowl and microwave in 30-second intervals. Remove the bowl at each interval and stir well. Repeat until the chocolate has completely melted. Stir until completely smooth.
2. Once melted, allow the chocolate to cool down to room temperature, about 5 minutes.
3. In a medium mixing bowl, cream the butter with a hand mixer until smooth. Add in the cooled dark chocolate and beat together until combined.
4. Slowly add in the powdered sugar and beat until fully combined.
5. Pour in the heavy whipping cream and add a pinch of salt. Continue to beat for an additional 10-15 seconds.
6. Transfer the chocolate buttercream to a piping bag fitted with a star tip (or any other tip you may have). Pipe the butter cream into the flat side of half of the macaron shells. Start from the center and move to the edges, leaving a little space on the edges. Top each piped macaron with on of the remaining macaron shells. 
7. Place macarons in an airtight container in the refrigerator overnight to mature (which allows the filling to soften the shells and flavor them). Bring them back to room temperature when ready to serve.