Preheat the oven to 175°F (80°C);
Weigh the egg whites directly in the bowl of the stand mixer and whisk at medium speed (speed 6 on a KitchenAid);
Add 1 cup (220g) of sugar but only a little at a time. Let the mixer run for a couple of minutes and then increase the speed (to 8);
Add the lemon juice and beat at a high speed (10) for about 10 minutes until stiff peaks form. Test your foam with a visual test—if you turn the bowl upside down, the foam shouldn’t fall out. The foam should be glossy;
If you have a pastry bag, fill it with foam by adding it carefully to the bag. Use the star tip and pipe out the foam into 1-inch (3 cm) mounds onto a parchment-lined baking sheet. Keep them uniform so that they bake evenly. If spooning them out, keep them as high (in mounds) as possible. Remember to leave enough space between them because they will increase in size. Meringues must be baked as soon as they are spooned or piped out.
Bake them on a parchment-lined cookie tray in a static oven for 2 hours so that they dry very slowly. Meringues are done when the center is dry. Let them cool down completely and remove them from the tray. As their baking is quite long you should prepare the meringues the day before and leave them in the oven until it cools down completely.