Add the aquafaba and white vinegar to a stand mixer, or mixing bowl. Whisk on high-speed until it starts to get white and foamy. Add the beetroot powder and whisk again until it starts to form soft peaks. Slowly pour in the granulated sugar and keep whisking until it forms stiff peaks.
In another bowl, mix together the powdered sugar and sifted almond flour. Transfer half of the almond flour mixture to the bowl of whipped aquafaba and gently fold it using a spatula. Once incorporated, add the rest of the almond flour mixture and fold the batter again (in a circle figure). At first the batter will be quite thick like a brownie batter, keep folding until the batter becomes shiny and stop once it falls into ribbons when holding the spatula up.
Transfer the mixture to a piping bag fitted with a 1-inch tip. Pipe ovals (2-inch long) onto a baking sheet lined with parchment paper, leaving about 1.5-inch between each one. Tap the baking sheet 4-5 times on your counter to remove any air bubble.
Let the macaron shells dry at room temperature for about 50 minutes.
20 minutes before, pre-heat your oven to 270°F (130°C). Please note that this temperature can change depending on your oven, you might have to adjust it for your next batches.
Bake the macarons for 25 minutes. Once you see the macarons has developed a feet, turn down the oven to 230°F (110°C). Then turn off the oven and let the door slightly opened. Leave the macarons inside the oven for another 15 minutes.
Remove from the oven and let the macarons cool completely before removing them from the baking sheet.
Pipe the chocolate ganache onto a macaron shell and sandwich with another macaron. Repeat with the remaining macarons and ganache. You can enjoy immediately or let them "rest" for a few hours.
To decorate, melt dark chocolate over a double boiler. Once melted, transfer to a piping bag and pipe the melted chocolate on top of each macaron.
Macarons will keep in the refrigerator in an airtight container for up to 3 days.