Butter a 9-inch round pie plate or cake pan.  Set aside.

Preheat the oven to 375 degrees.

To make the dough:

In the bowl of an electric mixer, combine the water, buttermilk, sugar, melted butter, and eggs. Stir gently until well combined.

Sprinkle in the salt, yeast, and 4 ½ cups of flour.

Mix the dough until well combined and begins to pull away from the sides of the bowl.  If it feels too sticky, add more flour, 1 tablespoon at a time, and then set the mixer to low and knead the dough for 10 minutes.

Allow the dough to rest for 10 minutes.

Meanwhile, make the filling.  

In a medium bowl, stir together the melted butter, brown sugar, granulated sugar, and cinnamon.  Set aside.

On a lightly floured surface, roll the dough into a 12×16-inch rectangle.

Use an offset spatula to spread the filling evenly over the top of the dough.

Starting at the long side, roll the dough up into a cylinder.

Use a sharp knife to cut the roll into 12 slices.

Place the slices in the prepared pan.

Bake in a preheated oven for 15-20 minutes until golden.

While the rolls bake, make the frosting.

In a medium bowl, beat the butter and cream cheese together until light and fluffy.

Pour in the vanilla and spoon in the powdered sugar.

Continue to beat the frosting until well mixed.

Add the heavy cream, 1 tablespoon at a time, until you reach the desired consistency.

Spread half of the frosting on the rolls while they are hot.

Allow the rolls to come to room temperature and then spread the remaining frosting on the rolls.