Overnight Chocolate-Hazelnut Breakfast Buns

Ingredients

• For the dough:
• 16 ounces all-purpose flour, such as Gold Medal, plus more for rolling
• 3 1/2 ounces sugar
• 2 teaspoons instant yeast, such as SAF
• 2 teaspoons Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 1/4 teaspoon baking soda
• 4 ounces unsalted butter
• 4 ounces milk, any percentage will do
• 8 ounces plain, unsweetened, strained Greek yogurt, such as Fage
• For the filling:
• 12 ounces homemade Nutella, creamy or crunchy
• 4 ounces skinned toasted hazelnuts, roughly chopped, or more to taste
• For the frosting:
• 4 ounces mascarpone
• 4 ounces heavy cream
• 1 3/4 ounces plain or toasted sugar
• 1/8 ounce vanilla extract, or more to taste
• 1/4 teaspoon Diamond Crystal kosher salt, or more to taste; for table salt, use about half as much by volume or the same weight

Directions

1. For the dough, add the flour, sugar, yeast, salt, and baking soda to a stand mixer bowl and stir them together. In a 2-quart saucier set over low heat, melt the butter, then mix in the milk and yogurt and bring the mixture to about 80 degrees F, or 27 degrees C. Pour the warm dairy mixture into the dry ingredients and stir until the dough looks very dry and ragged. With the dough hook attached, knead on low for about 20 minutes, until the dough is smooth, elastic, and can be stretched gently into a thin, slightly uneven sheet without ripping.
2. Cover the bowl with plastic and leave the dough at around 70 degrees F, or 21 degrees C, for about 1 1/2 hours, until it feels light and airy and has grown to about 2 times its starting size. If it still seems heavy, tight, or too springy, which can happen in colder weather, give it 15 more minutes and test again.
3. Set the dough on a lightly floured work surface, sprinkle the top with flour, and roll it into a 13-inch square. Use an offset spatula to spread the homemade Nutella evenly over the dough. Scatter the hazelnuts over the filling, then roll the dough into a log and set it seam side down.
4. Use an 8-inch piece of butcher's twine, plain thread, or unflavored dental floss, sliding it under the log until it reaches the center. Cross the ends over the top and pull firmly to split the log into 2 pieces. Cut each piece into 6 slices, each 1-inch thick, and arrange them in an aluminum baking pan, 9- by 13- by 2-inch, lined with parchment, or in 2 round cake pans, each 8-inch by 3-inch.
5. Cover the rolls with foil and refrigerate for an overnight chill, or for as long as 48 hours. While they chill, make the frosting by combining the mascarpone, cream, sugar, vanilla, and salt in the stand mixer bowl with the whisk attached. Whip on medium speed until the sugar dissolves and the frosting turns thick, fluffy, and able to hold medium-soft peaks. Adjust with more salt and/or vanilla to taste, if needed. Spoon the frosting into a disposable pastry bag or another airtight container, then refrigerate until needed, for up to 48 hours.
6. Place a rack in the middle of the oven and heat to 350 degrees F, or 180 degrees C. While the oven warms, let the buns sit at room temperature. Once the oven is ready, bake the buns with the foil on until they are risen, set, and still pale, about 30 minutes. If using darker pans, take a look at the buns a little earlier. Remove the foil and keep baking until the tops are lightly browned, about 15 minutes more. Cut a corner from the frosting bag and pipe it over each bun, or spoon the frosting on instead. Serve right away, since the buns do not hold up well over time.