Conchas de Chocolate (Chocolate Concha Sweet Buns)

Instructions

1. In a stand mixer bowl, combine the bread flour, instant yeast, granulated sugar and salt. Add the lukewarm whole milk, eggs and vanilla extract and knead with the dough hook on medium-low until a smooth dough forms, 7 to 8 minutes.
2. Add the softened unsalted butter a piece at a time and knead 5 to 6 minutes more, until the dough is soft, elastic and stretches thin without tearing.
3. Cover the bowl and let the dough rise in a warm place until doubled, 1 1/2 to 2 hours.
4. Meanwhile make the topping: beat the vegetable shortening and powdered sugar until creamy, then mix in the all-purpose flour and cocoa powder and knead briefly into a smooth paste, like play dough. Cover and set aside.
5. Turn out the dough, divide it into 12 pieces (about 83 g each) and roll each into a tight, smooth ball. Set 6 on each lined baking sheet, well apart, and flatten them slightly.
6. Divide the topping into 12 portions (about 25 g each). Press each between two sheets of plastic wrap into a 9 cm disc, lay it on a bun and press gently so it clings. Score a shell pattern with a concha cutter or the back of a knife, cutting through the topping but not into the dough.
7. Cover loosely and proof until the buns are puffy and the scoring has opened slightly, 45 to 60 minutes. About 20 minutes before they are ready, heat the oven to 350°F (175°C) with racks in the upper and lower thirds.
8. Bake both sheets, swapping and rotating them halfway, until the bottoms are golden and the buns sound hollow, or read 190°F (88°C) inside, 18 to 22 minutes. The topping should stay matte and not darken much.
9. Cool on a rack at least 15 minutes before serving.