Make the Dough: In a large measuring cup, whisk the buttermilk, melted butter, and eggs together until combined. In a large bowl, whisk 4 cups all-purpose flour, sugar, yeast, and salt together. Make a well in the center of the bowl and pour the buttermilk mixture in the center. Spoon the flour with a wooden spoon into the center until the flour is moistened and has a shaggy look to it. Turn the dough onto a lightly floured surface. Pour the remaining 1/4 cup of flour next to the ball of shaggy dough. Knead the dough, dusting your hands periodically with the flour until the dough is smooth and elastic, about 10-12 minutes. The dough should be tacky to the touch, but not sticky. Place the dough in lightly buttered bowl and wrap the bowl tightly with plastic wrap. Let the dough rise in a warm, draft-free place until the dough doubles in size, about 2 to 2 1/2 hours. Fill the rolls: Liberally grease a 9x13 inch baking pan or Pyrex dish. Sprinkle the pan lightly with granulated sugar and set aside. In a small bowl, mix the granulated sugar, cocoa powder, salt, and melted butter until a paste forms. Turn the dough onto a lightly floured surface and press or roll the dough to a 12x16 inch rectangle. With a small offset spatula spread the cocoa mixture, leaving a small 3/4 inch border along the perimeter of the dough. Press on the filling to help it adhere to the dough. Loosen the dough from the counter using a bench scraper (or metal spatula), and from the long end, roll the dough very tightly into a long cylinder. Pinch the seam closed and roll the log seam side down. Slice the cylinder into 12 evenly sized rolls (about 1½ inches wide) using a serrated knife. Arrange the rolls cut side down in the prepared baking pan and wrap with plastic wrap. Let rolls rise in a warm place until the rolls have doubled in size, about 1 to 1½ hours. The rolls will press into one another. While the rolls rise, preheat the oven to 350° Fahrenheit. Adjust the oven rack to the middle position. When rolls have risen sufficiently, remove plastic wrap and place in the oven. Bake the rolls until golden, about 25 to 30 minutes. Remove rolls from the oven and allow to cool slightly before glazing. Make the glaze: Whisk the confectioners’ sugar, cocoa powder, milk, and vanilla extract in a small bowl until smooth. Remove rolls from pan and place them in a wire rack that sits over a parchment lined cookie sheet. Glaze rolls and serve.