For the dough:
Warm buttermilk in a microwave or on the stove until it reaches 100°F. Whisk in 2 tablespoons of sugar and the packet of yeast, and let sit for 5 minutes. The yeast should begin to bubble.
Meanwhile, place the remaining 1 cup of sugar, flour, baking powder and salt in the bowl of a stand mixer fitted with the paddle attachment. Add the buttermilk mixture to the flour mixture and stir on low speed to combine.
Add the eggs one at a time and continue mixing on low until the dough just comes together. Switch to the dough hook attachment and turn the mixer to medium speed. Knead until the dough is very sticky and coming together, about 4-5 minutes, occasionally scraping down the sides of the bowl with a spatula.
With the mixer running, add the softened butter 1 tablespoon at a time, allowing each addition to become fully incorporated into the dough. When all the butter is added, continue kneading for 1–2 minutes longer. The dough should be very soft and sticky at this point.
Grease a 4.5 qt. Chef’s Oven, Braiser or Dutch Oven with butter, and transfer the dough to the pot. Cover with the lid and allow to rest for about 2 hours in a warm place until it is doubled in size, or place in the refrigerator to rest overnight.
For the filling:
Meanwhile, melt butter in a saucepan set over medium-low heat, and cook until butter is just starting to brown, about 4 minutes. Remove from the heat and add brown sugar, cinnamon and salt. Stir to combine and set aside until ready to assemble cinnamon roll.
For the cinnamon roll:
If dough is in the refrigerator, remove it about 2 hours before forming the cinnamon roll to allow dough to come to room temperature.
Turn dough out onto a flour coated work surface, and roll into a 20-inch by 15-inch rectangle. Spread the filling evenly over the surface of the dough, then cut the dough into 2 inch–thick strips (about 6–7 strips).
Roll up one of the strips into a spiral and place it in the center of the pot. Then, carefully wind the next strip around the first strip in the pot. Continue with more strips, winding them around the central roll, until you have one large cinnamon roll. Cover the pot with the lid and allow dough to rest again in a warm spot until doubled in size, about 1 hour.
Preheat oven to 350°F. Place pot in the preheated oven uncovered, and bake cinnamon roll until cooked through, puffed and browned on the top, about 30–35 minutes.
For the glaze:
While the cinnamon roll is baking, make the glaze. Stir together powdered sugar, buttermilk and salt until smooth.
Remove the pot from the oven and drizzle the glaze over the top of the hot cinnamon roll for serving.