Add the soda-vinegar mixture to the egg whites, whisk together.
In another bowl, whisk egg yolks with sugar.
½ cup sugar
Incorporate the egg yolk and sugar mixture with whisked egg whites.
Gradually add 1 cup of flour.
3 cups all-purpose flour
Add soft butter, and the rest of flour. Combine with spatula or spoon.
¾ cups butter
Knead the dough. Shape it into the disc, wrap and leave the dough for 15 min in the fridge.
Divide the dough into the small pieces. Roll between your palms to make a ball.**
Put the dough ball in the walnut shell and push with your fingers. You should make thin skin on each walnut shell and cover the sides, because it will shrink, when baking.
Make all the shells and bake for 8-10 min until golden. Let the shells cool. Bake the second batch.
Remove cookies form the shells. Using a very sharp knife, carefully cut down the edges of cookie to make it look smooth.
1-2 tins caramelized condensed milk (Dulce de Leche)*, 1 handful walnuts
Fill shells with caramelized condensed milk, add a half of walnut in the middle. Close cookies, gently pressing together. Use your fingers to wipe around the center excess condensed milk.
Video
Notes
* See directions in the post on how to make/boil condensed milk, if you can't find it.**Alternatively, thinly roll the dough and cut with walnut shell. Then press it with your fingers.Store cookies in an air-tight container at room temperature for 1-2 day or in the fridge - for two weeks.