In a small bowl, put the warm water with the yeast. Mix a little and let it sit for 10 minutes for the yeast to activate.
Meanwhile, on a clean surface put the flour with the rest fo the suagr, salt and powder milk. Mix these ingredients and make a hole in the middle of the mixture.
Add in the eggs, egg yolk and butter and start mixing from the inside out, trying to integrate all the ingredients.
Mix in the yeast mixture to this and knead using your hands, by punching and folding the dough onto itself for 15 minutes uuntil you get a soft and elastic dough (all this process can also be done using an electric mixer with thd dough hook on).
Put the dough in a bowl with a little oil so it does not stick to the bowl and for it to not dry. Then cover the bowl with kitchen plastic wrap or a kitchen towel.
Let it rest at room temperature in a somewhat hot spot for about 1 hour and 30 minutes until it doubles its size (this could take longer, depending on your kitchen´s temperature).
In a big bowl, put all the ingredients and knead for 3 minutes until a soft dough forms.
Divide this dough into two. Add the cocoa powder to one of them and knead using your hands until fully integrated. This way we eill get two different flavored coverings: vanilla and chocolate.
Wrap each covering flavor with kitchen plastic wrap and refrigerate them until needed.
One the dough has risen and doubled its size, put it on the kitchen countertop with some flour and cut it into 8 or 9 same size pieces.
Form small balls with each piece of dough and put them (separated from each other) on a rectangular pan of about 18 x 13 inches (46 x 33 cm) lined with parchment paper.
Flatten each ball using your hands and cover them with kitchen plastic wrap or a kitchen towel to let them rest for 15 minutes.
Take the sweet covering doughs out of the fridge and roll it out using a rolling pin on a floured surface until it is about 0.12 inches (3 mm) thick. Cut this into circles using a cookie cutter (about the same size in diameter as the dough balls) and put these sweet circles on top of each dough ball.
Using a pizza cutter or a sharp knife, make cuts on the top of each concha´s covering to make it look like a seashell (you can also do this with a special cutter made for conchas).
Cover the conchas again with kitchen plastic wrap and let them rest for 1 hour until they double in size. Preheat the oven to 375º F (180º C).
Once they double in size, bake for 20 minutes until they are slightly golden brown. Take out of the oven and let them cool down for about 10 minutes before eating.
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