Start by gathering and measuring all the ingredients to ensure a smooth preparation process.
For the bread, pour the warm water into a large mixing bowl and sprinkle the yeast over it. Allow the mixture to sit undisturbed for about 5 minutes until the yeast becomes foamy and creamy.
Add 2 cups of the flour, evaporated milk, sugar, melted butter, egg, and salt into the yeast mixture. Stir until the ingredients are well incorporated and a sticky dough begins to form.
Gradually mix in the remaining 2 cups of flour along with the ground cinnamon. Continue to blend until the dough pulls away from the sides of the bowl and comes together.
Transfer the dough onto a floured surface. Knead by hand for about 6 to 8 minutes until it becomes smooth, elastic, and slightly tacky. Place the kneaded dough into a large greased bowl, turning it once to coat all sides with a thin layer of oil.
Cover the bowl loosely with a clean towel or plastic wrap and let it rise in a warm, draft-free area until it doubles in size, which should take around 1 hour.
While the dough is rising, prepare the topping. In a medium bowl, beat the softened butter and sugar together using an electric mixer until the mixture becomes light and fluffy.
Gradually stir in the flour to create a dense, workable paste.
Divide the paste equally into two portions. To one portion, blend in the cinnamon for a warm, spiced flavor. To the other, mix in the vanilla extract for a sweet, aromatic finish.
Once the dough has doubled, punch it down gently and divide it into 12 equal pieces. Shape each piece into a smooth ball and arrange them on a greased cookie sheet, leaving about 3 inches of space between each one to allow room for expansion.
Divide the two toppings into 6 pieces each, shaping each into a flat disc. Place one topping disc over each dough ball, pressing lightly to adhere. Using a sharp knife, carve decorative grooves into the topping to mimic the appearance of a seashell.
Cover the assembled conchas loosely and let them rise once again until they double in size, about 45 minutes.
Preheat your oven to 375°F (190°C) towards the end of the second rise.
Bake the conchas in the preheated oven for approximately 20 minutes, or until they turn lightly golden and the kitchen is filled with a sweet, buttery aroma. Let them cool slightly before serving.