1. First, make the blueberry sauce: in a small saucepan, combine all the ingredients, and cook over low heat until blueberries release their juices, about 5 minutes.
2. Transfer the blueberry sauce to a blender and pulse in blender until semi smooth. Set aside until needed.
3. Combine the tapioca flour, eggs, yacon, avocado oil, and salt in a bowl, stirring until smooth. Set aside.
4. Pour about 1 inch of avocado oil into a small saucepan. Heat over medium heat until oil shimmers (350˚). Spoon the batter into a sandwich bag or pastry bag. Once the oil is shimmering, cut the top of the sandwich bag, if using.
5. Now quickly drizzle the batter into the hot oil, overlapping to make that classic funnel cake squiggle.
6. Allow the underside to brown, around 1 minute, then, using a flat slotted spoon, flip the funnel cake over to brown the other side.
7. Remove from the oil and place on a towel lined plate.
8. Serve hot, drizzled with blueberry sauce.