Preheat the oven to 180°C. Spray a baking dish with cooking spray. Add a large pinch of salt to the egg whites and beat with an electric mixer on low speed until stiff peaks form, 2 to 3 minutes.
Place the egg whites in the prepared baking dish. Make 6 small wells with the back of a spoon. Bake the whites until they are firm, no longer wet and just beginning to turn brown, about 6 minutes.
Gently pour 1 yolk into the well of each white. Bake until the edges of the yolk just start to set while still being runny, 3 to 4 minutes. Season with salt.
