Prepare Macaron Shells:
Clean your mixing bowls, whisks, and other tools with a bit of white vinegar on a paper towel to remove any grease.
Line two baking sheets with silicone macaron mats or parchment paper. Fit a piping bag with a round tip (Wilton 2A) and set aside.
Sift the almond flour, powdered sugar, and black cocoa powder together twice to remove any clumps, then whisk to fully combine.
Using a double boiler, heat the granulated sugar and egg whites over simmering water, whisking until the sugar dissolves and the mixture becomes frothy (about 5-6 minutes). Check by rubbing the mixture between your fingers to ensure there are no sugar granules left.
Transfer the mixture to a stand mixer fitted with a whisk attachment. Whip on high speed until soft peaks form, then add the salt and vanilla extract. Continue whipping until stiff peaks form (about 10 minutes). The meringue should look glossy and hold its shape.
Gently fold the dry ingredients into the meringue, pressing the mixture against the sides of the bowl while folding. Midway through, add the black gel food coloring. The batter should flow like lava and form ribbons.
Pipe and Rest the Macaron Shells:
Transfer the batter to a piping bag. Pipe 1.5-inch circles onto the prepared baking sheets. Tap the baking sheets on the counter 3-4 times to release any air bubbles.
Let the macaron shells rest for 35-45 minutes until they are dry to the touch. Preheat the oven to 300°F during the last 10 minutes of resting.
Bake the Macaron Shells:
Bake one tray at a time for 16 minutes, rotating the tray halfway through baking. Allow the macarons to cool completely before removing them from the mat.
Prepare Vanilla Cream Filling:
In a mixer, beat together the butter, vegetable shortening, powdered sugar, and vanilla extract on low speed until smooth and fully blended.
Assemble the Macarons:
Pipe the vanilla cream filling onto one macaron shell, then gently press another shell on top. Repeat until all macarons are assembled.
Store and Serve:
Store the macarons in an airtight container in the refrigerator for 2-3 days to let the flavors mature. Enjoy!