01 - Bring a medium saucepan of salted water to a boil. Add cubed potatoes and cook for 12 to 15 minutes, or until fork-tender. Drain thoroughly and mash until completely smooth.
02 - While the potatoes are still warm, thoroughly incorporate the mozzarella, parmesan, black pepper, garlic powder (if using), and melted butter. Allow the mixture to cool to a comfortable handling temperature.
03 - In a large mixing bowl, combine glutinous rice flour and salt. Slowly add water, stirring until a smooth, pliable dough forms. If the dough feels dry, add water a teaspoon at a time.
04 - Divide both the potato filling and mochi dough into 10 equal portions. Flatten a portion of dough in your palm, place a portion of potato filling in the center, and seal the dough around the filling. Repeat with remaining portions.
05 - Heat neutral oil in a non-stick skillet over medium-low heat. Place mochi balls seam side down and fry for 2 to 3 minutes on each side, turning until all surfaces are golden and crisp.
06 - Transfer fried mochi to a plate and let cool slightly. Serve warm for best texture.