In a small saucepan on medium heat, mix the milk and the baking ammonia. Stir and just warm it up. Don’t boil it. Set aside.
In another smaller saucepan on low heat, melt ¼ cup butter. Set it aside to cool. It will be used for kneading the dough.
In a large mixing bowl or bowl of a stand mixer fitted with the whisk attachment, add egg whites and beat on medium speed for about 5 minutes until the mixture is shiny with stiff peaks. Set aside.
Beat on medium speed, 1 cup softened butter, egg yolks, sugar, and vanilla extract until sugar is completely dissolved.
Use a spatula to slowly and gradually incorporate the two mixtures (egg whites and egg yolk with butter-sugar). Add the milk and baking ammonia mixture and stir to incorporate.
Keep 1 cup flour (it will be used for kneading the dough).
Preheat oven to 392°F (200C°) and line a large cookie sheet with parchment paper.
Add gradually the remaining 7 cups of flour to the main mixture about a half cup each time. First, use a spatula to incorporate and when the dough is firm use your hands. Grease your hands with the melting butter and pour gradually the rest in the dough. Mix well until all ingredients are well combined. If the dough is super sticky start using more flour. We need a sticky but not runny dough.
If the dough is super sticky and you can hardly handle the dough, use more flour. You need only 1 teaspoon each time. Incorporate it and see if it needs more. Please note that the dough should be sticky but not runny. To see if the dough is ready, shape a cookie and if it keeps its form, you are good to go. Otherwise, add more flour.*
Shape the cookies as desired but it is important that they are all pretty much the same size. Place them on the sheet leaving at least 1 ½ inches (4cm) space between them.
Prepare the egg wash by mixing together egg yolks, milk, and water. Brush on top of each cookie.
Bake for about 20-25 minutes until golden brown.