Sift the almond flour and powdered sugar together using a fine mesh sieve.
Place the bowl over a pan with barely simmering water. Make sure the water isn’t touching the bottom of the bowl, otherwise the whites may cook. Also make sure the sugar is completely dissolved by the end.
Transfer the mixture to a mixer. Whip until the meringue is stiff. The peak should be shooting straight up, not bending down to the side.
The perfect batter will be flowing off the spatula slowly and effortlessly, the lava effect. You should be able to draw several figure 8s with the batter that’s flowing off the spatula.
Transfer the batter to the pastry bag. When you're done piping, bang the tray against the counter or against the palm of your hand a few times each, and pop any air bubbles with a toothpick.
To fill the macarons, I have available over 150 macaron fillings and ideas on the blog.