In the bowl of a stand mixer fitted with the dough hook, add the water, buttermilk, sugar, melted butter, and yeast. Mix. Let sit for 15 minutes. Add salt, eggs, and flour. Mix for 8-10 minutes. After mixing, cover the bowl with plastic wrap and allow the dough to rest for 10 minutes.
In the meantime, prepare the filling. In a small bowl add the sugar, orange zest, and orange juice. Stir to combine.
Preheat the oven to 400°F. Place a silicone baking mat or parchment paper on a baking sheet. Alternatively, you can spray the baking sheet with cooking spray. Spray your countertop with cooking spray ( I used Bakers Joy). Roll the dough into a 14"x18" rectangle. Using the back of a spoon, smear the softened butter over the top of the dough. Sprinkle the orange sugar filling evenly over the softened butter.
Starting with the long side, roll the dough into a log so that then resulting cinnamon roll measures 18" in length. Cut into 12 large rolls. Place the rolls onto the prepared baking sheet. 3 rolls across, and 4 rolls down. Lightly cover the orange rolls and set them in a warm place to rise for 20 minutes.
Bake for 20-24 minutes or until golden brown and cooked throughout.