In the bowl of a stand mixer whisk together water, buttermilk, granulated sugar, melted butter, and yeast in a bowl. Allow to proof for 15 minutes.
1 cup warm water, 3/4 cup buttermilk, room temperature, 1/2 cup granulated sugar, 1/4 cup unsalted butter, melted, 3 tablespoons Active dry yeast
With the dough hook attached add the salt, eggs, and 5 cups of flour and knead for 10 minutes. Only add just enough of the remaining 1 cup of flour to make the dough pull away from the sides of the bowl. DO NOT ADD TOO MUCH FLOUR. They will be dense and tough.
Roll dough out on to lightly floured or greased surface into a 12 x 16-inch square. Spread the filling over the dough leaving about 1/2" along the edges. From the long edge tightly roll up, pinch to seal the seam. Cut into 12 large rolls.
Place rolls in a lightly buttered 9x13 baking dish, cover with parchment paper. Let rise for 15 minutes. Preheat the oven to 400F, while rising.
Bake at for 15-20 minutes. You made need to tent with foil if they start to get too brown before done baking.
Frosting:
In a medium-size bowl mix together the powdered sugar, orange zest, vanilla and enough fresh orange juice to make desired consistency to spread. Spread or drizzle over the warm rolls.