Combine the water, buttermilk, sugar, and melted butter in the mixer bowl. Stir to lower the temperature to 95 degrees.

Sprinkle the yeast on the top of the water mixture. Lightly press it with a fork into the liquid to moisten it. Let it sit to proof for 15 minutes until puffed and frothy.

Add in the eggs, and salt. Fold in the flour, and mix slowly using a dough hook until flour is incorporated.

Set the mixer on med-low speed and mix/knead until smooth. Let the dough rest for 10 minutes while you make the filling and preheat the oven.

Prepare the filling by combining the brown sugar, sugar, and cinnamon in a small bowl and mixing it with a fork.

Preheat oven to 375 degrees and grease a 7½ x 11 baking dish.

Roll dough out on a lightly floured surface into a flat & even layer. Brush with melted butter and then sprinkle the filling mixture on top.

Roll tightly on the long side and then cut the log into 6 large rolls. Place them in the prepared dish and bake for 15-20 minutes.

Remove and allow them to cool slightly while you mix the icing.

Prepare the icing by combining all ingredients in a small bowl and whisking well until you reach the desired consistency. Drizzle over the top of the rolls while they are still warm.