Start by preparing the dough. Mix together the flour, butter, water, egg and sea salt. Once the mixture has a consistent texture, press into a ball and let rise in the refrigerator.
To make the stuffing, start by warming the oil in a medium sauté pan on high heat. Reduce the heat to medium heat and cook down the onions with a pinch of sea salt and chili flakes until they have caramelized, about 15-20 minutes - stirring frequently. Now toss in the sweet potatoes with a splash of water and cook until softened, about 15 minutes. Keep adding splashes of water, so that they don’t stick to the pan. Once the sweet potatoes have fully cooked, add in the mushrooms and cook down for another 5 minutes. Once everything is cooked and with the back end of a fork, mash some of the sweet potatoes into a paste.
Now, take out the empanada dough from the refrigerator, flatten, and shape into around 4-inch circles. Add the stuffing mixture into the dough, seal and bake for 20-25 minutes on 375°F, or until the tops of the empanadas are golden and crispy. Serve as is or dipped into a chimichurri sauce, which can be made by blending together the cilantro, onion, green pepper, garlic, sea salt, olive oil, and white wine vinegar. Enjoy!