Topping: 100 g all-purpose flour (3/4 cup + 1 tbsp)
100 g powdered sugar (3/4 cup + 2 tbsp)
80 g soft butter or vegetable shortening (6 tbsp)
1 tsp vanilla; 1 tbsp cocoa for chocolate ones
How to make it
Dough (15 min plus 1 hr 30 min): Knead flour, sugar, yeast, salt, cinnamon, milk, eggs and vanilla for 5 minutes, then knead in the butter until smooth and soft, about 8 minutes. Cover and rise until doubled, about 1 1/2 hours.
Topping (5 min): Mix flour, powdered sugar, butter and vanilla into a smooth paste. Split it and knead cocoa into half for chocolate conchas.
Shape (15 min): Divide the dough into 12 balls (about 80 g each) and set them on lined trays. Press each slightly flat.
Top (10 min): Roll a walnut of topping into a ball, flatten it between plastic wrap into a 9 cm disc and lay it on a bun. Score it with a concha cutter or a knife in curved lines like a shell.
Proof (45 min): Proof until puffy, 45 minutes to 1 hour.
Bake (18 to 20 min): Bake at 180C (350F) 18 to 20 minutes, until the bottoms are golden; the topping should stay pale.
Tips
Score the topping, not the dough underneath.
For a guava roll, roll the dough out, spread with guava paste and cream cheese, roll up and slice.