In a small saucepan set over low heat, combine the milk and butter. Cook until the butter is melted. Add the agave syrup, honey and apple sauce. Transfer it to a bowl and add the yeast. Make sure all the yeast is wet and let it rest for 10 minutes.
Add most of the flour (around 200 g) to the milk mixture, and using a spatula, mix just until combined. Cover the dough loosely with a damp towel and let this rest for 1 hour. The dough should double in size.
Add the rest of the flour, baking powder, cinnamon and salt. Mix it with dough hooks for 8-10 minutes.
Flour your work surface then turn out the dough and knead it for 1 minute until it comes together in a smooth ball. If the dough feels overly sticky, add more flour as needed, but do not over-knead the dough. Roll the dough into a rectangle.
Preheat the oven to 175 °C. Grease an 8- or 9-inch baking dish.
In a small bowl, whisk together the ingredients for the filling.
Brush the dough all over with the cinnamon-sugar mixture.
Beginning at the long end, tightly roll the dough up into a log. Trim off the edges then slice the log into 12 rolls. This can be easily done by using a dental floss.
Put the rolls in a baking dish. Bake for 25 to 30 minutes, till they are pale golden and baked through.
Meantime, make the frosting by mixing all the ingredients together.