Preheat the oven to 180ºC (356°F) and place the rack in the middle position.
Line a large rectangular baking tray with parchment paper and set aside.
Add the flour, salt and baking powder into a bowl and whisk together and set aside.
Add the whole egg, egg yolks, and sugar in a mixing machine with the whisk attachment. If you don’t have a mixing machine, you can use a bowl and hand beater, follow the same process.
Whisk ( Mixing machine) or beat ( hand beater) on high speed the eggs and sugar mixture for 12-15 minutes adding the lemon juice towards the last minute until mixture is light and fluffy, almost similar to a meringue texture.
Add flour slowly in portions into the egg mixture, folding it in from the bottom to the top, repeat until all the flour is incorporated, and well combined. Be careful not to over mix.
Using a tablespoon, deposit dollops of the batter onto the lined baking pan separating them apart by about 1 1/2 inch.
Bake in preheated oven for about 9-10 minutes or until the cookie is light golden brown in color.
Remove from the oven and carefully transfer the cookies using a flat spatula to a wire cooling rack, and cool for about 10-15 minutes then transfer to a larger plate before glazing. Note, Cookies will be very soft until they are completely cooled.
Repeat until all the batter is used up.
For the sugar icing glaze: Add the icing sugar, egg whites, and lemon juice into a medium-size bowl and whisk vigorously until the icing glaze is light, shiny, and well combined. If you notice the glaze is liquidy, add in another 1-2 tablespoons of icing sugar until it is a pasty consistency.
Glazing the cookie: To glaze the Doce Branco, spread the sugar glaze throughout the bottom first and set aside to dry for about an hour. repeat until all the bottoms of the cookies are glazed.
Once the bottoms are dried, glaze the top of the soft cookies, and using your three middle fingers, create a swirl on the surface which will give these cookies it’s distinctive seashell appearance.
You can also use the tip or back of a teaspoon creating three swirls along the top.
Set aside and let the glaze dry for another hour.
These cookies will keep well in an airtight containers for up to 2 weeks.