Sift ground almonds and powdered sugar through a fine sieve and mix them together.
Add 90 g of egg whites and mix to a homogeneous paste.
Put water and sugar together in a small saucepan and bring to a boil over medium heat, stirring constantly; the sugar should have dissolved before boiling. If it doesn't, take the saucepan off the heat briefly, stir it until the sugar dissolves, put it back on the heat and then boil it.
Alternatively, add any food coloring to the sugar syrup, stir it briefly and boil the sugar syrup over low heat (stop stirring) until it reaches 118 - 120 °C.
In parallel, start whipping the remaining 90 g of egg whites and salt with a food processor at medium speed.
Once the sugar syrup reaches 118 - 120 °C, take it off the heat and immediately add it slowly, in a thin stream to the whipped egg whites, continuing to whip the egg whites. Just before the sugar syrup reaches the necessary temperature, you can check if the egg whites already have a foamy consistency. If it is not, you can briefly turn the food processor on maximum speed. However, the egg whites must not be whipped into a solid mass when you add the sugar syrup. After adding the sugar syrup to the egg whites, continue to beat the mixture at maximum speed of the food processor for about 10 minutes, until the cream is firm and the mixing bowl with the meringue is no longer hot, but only warm when touched from the outside.
Add the meringue in batches to the almond mixture and gently and briskly fold it in in circular motions with a silicone spatula. You must keep making circular motions with the silicone spatula until you get a viscous almond dough that flows off the spatula in an unbroken strip. The dough should not become too runny, nor too firm. (Be sure to follow my tips and tricks for this here at the top of the post).
Fill the almond dough into a piping bag with a hole nozzle and place blobs about 2 inches in diameter on a baking sheet lined with parchment paper, leaving enough space between them.
Tap the baking sheet with the bottom straight down on the work surface a few times to remove any air bubbles from the blobs. Let the macaron shells sit at room temperature until their surface dries a bit and is no longer sticky. To check, touch a few macarons to the surface with your finger. The time to dry can vary greatly, depending on the room temperature and humidity. For me, it took 1.5 hours.
Preheat the oven to 150 °C top and bottom heat. Put the baking tray with the macaron shells into the oven and switch it to 140 °C. Bake the macaron shells for approx. 7 minutes, and they should have "feet". Remove them from the baking tray together with the baking paper onto the work surface and let them cool down.