1.  In your stand mixer with the whisk attachment, whisk the yolks, whole egg, sugar butter and buttermilk.  Add 2 C of flour along with the yeast and salt.  Whisk until moistened and combined.  Remove the whisk and replace with hook.  Add all but 3/4 C of the remaining flour and knead on low speed for five minutes.  Check the  consistency of the dough, add more flour if necessary; the dough should feel soft and moist but not sticky.  (I had to add 1/2 C)  Knead on low for 5 minutes more until the dough clears the sides of the bowl.  Transfer to an oiled bowl and allow to rise until double in volume, 2 1/2 to 3 hours.

2.  Combine the brown sugar, cinnamon and salt and set aside.  Grease a 9 x 13 glass baking dish.  Turn the dough onto a lightly floured work surface and roll into an 18 x 12 rectangle with the longest side near you.  Brush the dough with melted butter, leaving a 1/2 border along the top edge.  Sprinkle on the filling and gently press into the dough.  Beginning with the longest end near you, roll the dough into a tight cylinder.  Firmly pinch the seam to seal and very gently shape to create an even thickness along the cylinder.

3.  Using a serrated knife or dental floss, slice into 12 equal rolls.  Arrange rolls in the baking dish and cover tightly with plastic wrap.  Store in refrigerator overnight or up to 16 hours.

4.  Remove rolls from fridge and place in an oven that is turned off.  Fill a shallow pan 2/3 full of boiling water and set on the rack below the rolls.  Close the oven door and let the rolls rise until puffy, about 30 minutes.  Remove both pans from the oven and preheat to 350 degrees.

5.  Bake on the middle rack until golden brown, about 23-25 minutes.  Allow the rolls to cool slightly before icing.  Serve immediately.