For the dough:
3 large eggs
1⁄3 C. packed light brown sugar
3/4 C. buttermilk
2 tsp. kosher or 1 tsp. table salt
2 tsp. instant yeast
6 T. unsalted butter melted
4 C. all-purpose flour, plus more for dusting
For the sauce:
4 T. unsalted butter
2⁄3 C. packed light brown sugar
3 T. buttermilk
1 C. toasted pecans, coarsely chopped
1 pinch kosher salt
For the filling:
1 C. packed light brown sugar
1-2 T. ground cinnamon
1 tsp. nutmeg
2-3 T. unsalted butter melted
Make the dough by whisking the eggs in a large bowl. Add the brown sugar, buttermilk, salt, yeast and melted butter and whisk until homogeneous (the mixture may clump up a bit). Add the flour and stir with a wooden spoon until a cohesive ball of dough forms.
Turn the dough out onto a lightly floured surface and knead for 2 minutes, or until completely smooth and silky. Return to the bowl, cover with plastic wrap, and allow to rise at room temperature until roughly doubled in volume, about 2 hours.
To make the caramel pecan sauce, cook the butter and brown sugar in a small saucepan over medium-high heat, stirring occasionally until the sugar is completely dissolved and the mixture is bubbling, about 2 minutes. Add the buttermilk, pecans and salt and stir to combine, then pour the mixture evenly over the bottom of a 13-by-9-inch glass baking dish.
Combine the sugar and cinnamon for filling in a small bowl and set aside.
To assemble, turn the dough out onto a floured surface and lightly flour it. Shape into a rough rectangle with your hands and then, using a rolling pin, roll into a rectangle about 16 inches long and 12 inches wide, with a short end toward you.
Brush with the melted butter, leaving a 1-inch border along the top edge. Sprinkle with the cinnamon and sugar mixture and spread it with your hands until the buttered portion is evenly coated. Roll the dough up jelly-roll-style into a tight cylinder, using a bench scraper as necessary to assist you. Pinch the seam shut and turn the dough so that it's seam-side down. Use your hands to even out its shape.
Use a sharp knife to cut the roll into 12 even slices. The easiest way to do this is to cut it in half, cut each half in half, and then cut each section into thirds.
Nestle the 12 rolls with the swirl pattern facing up in the prepared baking dish, making sure the slices from the ends of the log go cut side down. Cover with plastic wrap and allow to rise until roughly doubled in volume, about 2 hours. The rolls should be well puffed and pressed tightly against each other.
While the dough is rising, adjust an oven rack to the middle position and preheat to 350°. Bake until the buns are golden brown and well puffed, about 30 minutes, rotating the dish once. Allow to rest for 5 minutes, then invert the buns onto a serving platter; scrape out any excess goo from the pan and spoon over the buns.