Place the egg whites, sugar and almond flour in a pot and mix while cooking for 10-12 minutes over medium heat. Cook until the texture starts to have a consistency that it takes about 10-15 seconds to spread when you mix it.
Once removed from heat, add the lemon’s juice if using and mix to cool.
When the mixture comes to room temperature use a cream bag to make walnut-sized macaroons on the oven sheet. They should be about 2-3 centimetres apart. Press a wet finger on top of each to flatten slightly.
Bake in a preheated oven at 130° Celsius (275° F) for about 25 minutes. Then increase the heat to 150° Celsius (300° F) and bake for an additional 10 minutes.
Make a toothpick test to check. Poke a toothpick into one of the macaroons, if it comes out clean, they are ready.
Prepare a damp kitchen towel. When out of the oven, place the oven sheet with the macaroons still on top of it on to this wet kitchen towel. This will make the bottom of the macaroons become humid and sticky. Leave on this kitchen towel for 2-3 minutes. Then stick two macaroons with the bottom sides facing each other. Set aside, the humidity will make them stick to each other.
After a few minutes, they are ready to serve.