Line 3 baking sheets with parchment paper. If you wish you can use a pencil to trace out the circles
Sift the almond flour and powdered sugar twice in a medium bowl.
In the bowl of a stand mixer with the whisk, whip the egg whites on medium until it starts to foam. Raise the mixer speed to high, and slowly stream in the granulated sugar. Continue whipping until you get medium peaks, about 5-7 minutes. Add your vanilla and food colouring.
Gently fold in half of the almond mixture. Once combined, add the remaining almond mixture and continue folding. When folding, you want to be bringing the batter around the sides of the bowl in order to deflate the batter. Continue doing this until your batter looks like lava
Transfer the batter to a pastry bag and pipe out the cookies onto your sheets. Bang (not too hard) each pan twice on your counter, this will get rid of any air bubbles.
Let the macarons stand at room temperature for 20-30 minutes, until they form a skin. If you touch them and they are no longer sticky, then they are ready to bake!
Preheat the oven to 300°F/150°C. Bake them one sheet at a time in the middle of the oven, for 18-20 minutes
Make Buttercream
In the bowl of a stand mixer with the paddle attachment, beat butter until smooth.
Add icing sugar and beat for 5 minutes, until fluffy. Add rum/brandy, vanilla, nutmeg, and salt for another minute. Use immediately.