Bring a large pot of salted water to a boil. Add the potatoes and cook for 15–18 minutes, or until fork-tender. Drain well and return them to the hot pot for 1 minute to remove excess moisture.
Mash the potatoes until smooth. Mix in butter, heavy cream, salt, black pepper, garlic powder, and onion powder. Allow the potatoes to cool for about 10 minutes.
Stir into the cooled mashed potatoes cheddar cheese, Parmesan cheese, parsley, and beaten egg. Mix until well combined.
Preheat the oven to 400°F. Grease or line a 12-cup muffin pan. Scoop about ¼ cup of the potato mixture into each muffin cup. Press a cube of mozzarella into the center. Cover with a little more mashed potato mixture and seal completely. Smooth the tops.
Brush each puff with melted butter. Mix the Parmesan and garlic powder together, then sprinkle over the tops.
Bake for 25–30 minutes, or until golden brown, crispy around the edges, and heated through. For extra browning, broil for 1–2 minutes at the end, watching carefully.
Notes
Ensure the potatoes are well-drained to avoid soggy puffs.
Feel free to experiment with different cheeses for varied flavors.
These puffs can be made ahead of time and frozen before baking.