Preheat your oven to 400 degrees and grease an 8 inch or 9 inch circle pan.
Start off with the wet ingredients. Add the milk and lemon juice to a medium bowl. Let it sit for 10 minutes while you gather your other ingredients. Combining the milk and lemon juice will create a homemade buttermilk. Then add the vanilla and melted butter. Whisk to combine.
Now combine the dry ingredients. In a large bowl add the flour, sugar, baking powder and cinnamon.
Then add the wet ingredients into the dry mixture. Mix with a spoon or spatula. Let the batter sit while you make your filling. This will allow the dough to thicken and make it workable.
Meanwhile, make the apple pie filling. In a small bowl combine all the filling ingredient: apple sauce, butter, sugar, apple and cinnamon. Mix until combined.
Now carefully roll out the dough on a floured surface. Using your hands or a roller press the dough into a large rectangle. Spread the apple filling in an even layer on top of the dough.
Roll the dough into a log. Since we are using a gluten free oat flour to make the dough, it make crack as you roll it into a log. Just be patient and gently roll it up, pinching together any cracks along the way. Once the dough is rolled into a log. Slice it in half with a very sharp knife. Then cut each half into 4 slices.
Add the 8 rolls to your prepared circle pan. Bake the rolls at 400 degrees for 20-22 minutes.
While the apple cinnamon rolls are baking, make the icing. Combine the butter, milk powdered sugar, and vanilla in a small bowl and whisk until smooth. Remove the rolls from the oven, let them cool for a minute or two then add the icing and enjoy!