- In a large mixing bowl, combine flour, sugar, yeast, and salt. 
- Add softened butter, warm milk, and eggs. Mix until a dough forms. 
- Knead the dough on a floured surface for about 10 minutes, until smooth and elastic. 
- Place the dough in a greased bowl, cover, and let rise for about 1 hour, or until doubled in size. 
- For the topping, mix together butter, sugar, flour, and vanilla extract until smooth. If making chocolate topping, divide the mixture and add cocoa powder to one half. 
- Divide the dough into 12 equal pieces and shape into balls. Place on a baking sheet. 
- Flatten a piece of topping dough and place it on top of each dough ball. Use a knife to cut shell patterns into the topping. 
- Cover and let rise for another 30 minutes. 
- Preheat the oven to 350°F (175°C). Bake for 15-20 minutes, or until the conchas are lightly golden. 
- Let cool before serving. Enjoy!