The Bojon Gourmet

Make the dough:
1 In a small saucepan, heat the buttermilk and cream together oven a medium-low flame, swirling occasionally, until steaming and small bubbles form around the sides of the pan; be careful not to let the mixture boil, or the buttermilk may curdle. Pour the mixture into the bowl of a stand mixer and let cool to just warmer than body temperature.
2 Whisk the yeast into the warm dairy and let stand 5 minutes. (Mine didn't foam up, I think because the acidity and fat prevent it from doing so, but the final dough still rose.)
3 Add the 2 1/2 cups flour, and the egg, butter, sugar and salt.Place the bowl on the stand mixer fitted with the dough hook (or mix in a large bowl with a wooden spooand mix on low speed for a couple of minutes until the dough comes together, scraping down the sides of the bowl once or twice. Increase the speed to medium, and mix for 7 minutes, adding flour by the tablespoon within the first couple of minutes until the dough mostly pulls away from the sides of the bowl. You'll know you've added enough flour when you can touch the dough briefly with clean, dry fingers and it does not stick. The finished dough will be somewhat soft and sticky.
4 Add the chocolate chunks and knead briefly on low speed just to incorporate.
5 Scrape the dough into a lightly oiled bowl at least double the size of the dough. Cover the bowl with plastic wrap or a heavy plate, and let the dough rise in a warm spot until doubled or tripled in bulk, about 2 hours. (An oven with a pilot light is a good spot.) Alternately, leave the dough in the fridge overnight, then bring to room temperature the next day and proceed with the recipe, making sure the dough has doubled in bulk.
Roll and bake the buns:
1 Scrape the dough out onto a lightly floured surface and roll it into a 10x12" rectangle with a long side facing you, dusting the dough, your hands, and the rolling pin with just enough flour to keep the dough from sticking.
2 Beat the remaining egg in a small bowl until completely smooth, then paint a strip of egg wash along the top, long side of dough. Roll the dough up into a log, pinch the seam to seal, and squish in the ends to make them even. Use a sharp chef's knife to cut the dough into 12 equal pieces. (I cut the dough in half, then each half into halves, then each quarter into thirds.)
3 Line a rimmed baking sheet with parchment paper. Place the dough rounds, cut-side-down, on the sheet pan, spacing them at least 2" apart. Cover the baking sheet either with another inverted, rimmed baking sheet, or slide it into a clean, plastic garbage bag. Let the buns rise until increased in size by a third, about an hour.
4 Meanwhile, position a rack in the center of the oven and preheat to 350º. When the buns have risen, brush the tops and sides with the egg wash, and sprinkle each one with a big pinch of coarse sugar.
5 Bake the buns until golden-brown on top, 25-35 minutes. Serve warm. Extras can be cooled and stored in an airtight container for up to 2 days. Re-heat in a 350º oven or toaster oven until warm, about 5 minutes.