Preheat oven to 425F. Poke holes in all potatoes after rinsing them then add to a baking sheet. Bake for 30 minutes until done. Set aside to cool. Keep oven on but move down to 375F.
For the Salsa: de-husk tomatillos and rinse. Add them to a large pan over medium-high heat. Add in broth, yogurt, onion, and salt. Cook the tomatillos for about 8-10 minutes, add garlic to the pan in final few minutes. Continue to add salt as you go. Once cooked, add to a blender and blend until smooth. Taste to see if more salt needs to be added then set aside.
In a large pan over medium-high heat, add olive oil. Add the thinly sliced onions and cook for 5 minutes until they turn soft and golden. Add salt then reduce heat to low. Stir occasionally and let cook for 25-35 minutes until they are gold and caramelized. Set aside.
While onions and potatoes are cooking, add all sour cream ingredients to a mixing bowl. Whisk until smooth. Set aside in fridge until ready to serve.
For the assembly, grab a baking dish and pour 1/4 cup of the salsa on the bottom. Smooth out so all the dish is coated. Heat your tortillas over a flame and set aside. Take one tortilla, lay flat in the baking dish that has the salsa, add 1 spoonful of the inside of the potato, the carmelized onion, and any other toppings. Slowly roll up the tortilla then push the rollup to one of the ends of the dish. Repeat with all tortialls until dish is full. Pour remaining salsa all over the tortillas once done. Add the shredded cheese. Place the dish back in the oven at 375F and bake for 30 minutes until cheese is melted.
Take enchiladas out of oven. Cut into serving portions with a knife. Divide to plates then top with avocado slices, homemade sour cream, and chopped cilantro