In a large, deep bowl, whisk together the eggs, milk, vanilla, cinnamon, salt, and nutmeg until well combined.
Preheat your griddle or large skillet over medium heat and coat with 1 Tbsp of butter.
Dip each half of the Hawaiian rolls into the egg mixture, allowing them to soak up the liquid, then let any excess drip off. Place the dipped rolls on the hot griddle.
Cook for about 2-3 minutes until they are golden brown, then flip them over and cook for another 2-3 minutes on the other side.
Once done, transfer to a plate and keep warm while you prepare the rest, adding more butter to the griddle as needed for the remaining rolls.
Serve the French toast warm, dusted with powdered sugar, and drizzle with maple syrup if desired.