Making the Dough:
Add flour, eggs, egg yolk, and salt to a mixer, fitted with the dough hook. Start the mixer on low speed.  Meanwhile, add yeast to water and stir until creamy and well dissolved.  Pour into the flour mixture and let the mixer continue to work, now over medium speed, for 3-4 minutes.

Add the butter, and continue to beat for another 3-4 minutes.  Lastly, add the sugar, and continue mixing for another 3 – 4 minutes or until the dough is gooey, sticky, elastic, and very smooth.

Turn dough out of the mixer, form into a ball, and place in a greased bowl.  Cover with plastic or a kitchen towel and let rise at a warm room temperature until doubled in size, 3-4 hours.  Note: After the bulk ferment, if you aren’t ready to shape and bake the conchas, you can place the dough in the refrigerator overnight.  Let it warm up to room temperature for at least 30 minutes before shaping the conchas.

Making the Sugar Shell Topping:
Combine the flour, powdered sugar, and organic sugar in a medium bowl. Cut in the butter until well combined. Start with 1/2 cup of butter, add more if the dough feels too dry.  Use your fingers, or a pastry blender if you prefer. Work in the vanilla.

Continue mixing until the sugar mixture forms a ball.  Divide the dough into two equal pieces. Stir in the cocoa powder and ground cinnamon into one of the doughs of sugar topping, mixing until well combined.  (The mixture might be sticky, but don’t add more flour.) Refrigerate the dough until ready to use.  Refrigerating the dough makes it easier to work with; however, if you refrigerate it too long, you will need to let it warm up to room temperature because it will be too stiff to work with.

Assembling the Conchas:
Grease heavy baking sheets with butter or vegetable shortening (or use parchment or a silpat). Rub a bit of butter onto your hands to make for easy rolling. Divide dough into 12 or 16 equal pieces and form into balls. Then, slightly press them flat, as in a thick disk. Leave about 2 inches of space between each of the conchas so they will have room to expand.

Divide your sugar topping into 12 or 16 equal pieces (the same number as dough balls).  Form each into a ball and flatten into a thin disk.  Place a disk on top of each dough ball and lightly press down.  The sugar should cover the whole surface—it will pull away from the edges as the dough rises.

If you have a concha mold, press it on the sugar topping.  If you don’t have one, cut through the sugar topping with a knife or the edge of a circle cutter, making shell-type lines.

Leave the prepared conchas in a warm area of your kitchen, uncovered, and let them rise again, for about 45 minutes to an hour or so, or until they’ve almost doubled in size.  Preheat the oven to 350° F during the last 15-20 minutes of rise time.

Slide the conchas into the oven and bake for about 20 minutes, or until the conchas are just golden around the edges and have fluffed up.  Be careful that your oven is not hotter than it should be, or the outsides will get very dark and the sugar topping will discolor.

Carefully remove to a wire rack to finish cooling.