Mix together water, buttermilk, sugar, melted butter and yeast in a bowl. Allow to sit for 15 minutes.
While yeast mixture is sitting. Cook your butter, diced apples and sugar in a saucepan over medium heat. Add ½ tsp cinnamon to apple mixture. Let simmer until sauce begins to thicken. Add 1 tsp flour as needed until you have a slightly thickened apple pie mixture. You don’t want it super runny or it will seep out when cutting your rolls. Filling should thicken more as it cools.
Add in salt, eggs and flour to the yeast mixture and mix for roughly 10 minutes. The dough should begin to pull from the bowl and be only slightly tacky. Allow to sit for 10 minutes.
In a small bowl mix together brown sugar and remaining cinnamon. Roll dough out on to greased countertop into a 12 x 16 inch square.
Sprinkle with brown sugar filling and then spoon on apple pie filling. Use a small spatula or icing spreader to spread apple filling around and roll up. Cut into about 18 large rolls about 1 inch thick.
Place rolls on a cookie sheet covered with a silpat or parchment paper. Let rise for 15 minutes Bake at 400 for 10-12 minutes.
Mix together frosting and spread on warm rolls.