Line two baking sheets with silicone baking mats or parchment paper. Set them aside.
Place almond flour, powdered sugar, Dutch cocoa powder, and salt into a food processor. Pulse on high about 10 times to ensure the mixture is fine. Sift the mixture through a fine-mesh sieve into a large mixing bowl. Discard any larger pieces.
In a stand mixer, beat room-temperature egg whites with vanilla extract and cream of tartar on high speed. After 1 minute, slowly add superfine sugar. Continue whipping for another 4-5 minutes until stiff peaks form.
Gently fold in 1/3 of the sifted dry ingredients into the whipped egg whites using a silicone spatula. Repeat with the remaining dry ingredients in two more stages. Be careful not to over-mix; the batter should flow like lava and form a ribbon that disappears within 10 seconds.
Fit a round piping tip (Wilton 1A) into a piping bag and fill it with the batter. Pipe 1-inch mounds of batter onto the prepared baking sheets, leaving 1-2 inches of space between each mound.
Tap the baking sheets onto the counter about 10 times to remove air bubbles. Use a toothpick to pop any remaining visible air bubbles.
Allow the macarons to dry at room temperature for 30-50 minutes, or until they’re no longer tacky to the touch.
Preheat the oven to 325°F (conventional setting).
Bake one tray at a time for 16-18 minutes. The macarons should not stick to the silicone mat or parchment paper when done. Let them cool completely on the sheets before removing them.
In a saucepan, heat the heavy cream until it simmers. Pour it over the semisweet chocolate in a heatproof bowl. Stir with a whisk until smooth. Let it cool to room temperature.
Transfer the cooled ganache to a piping bag. Pipe the ganache onto the flat side of one macaron shell, then sandwich it with another shell. Let the macarons rest in the fridge for a few hours or overnight.
Bring the macarons to room temperature before serving for the best texture.