Unwrap panettone and place on its side on a cutting board. Using a serrated knife, slice about 1/2 inch of the dome off the panettone so the top and bottom are both flat (set aside the dome piece for snacking). Turn panettone right side up and slice in half from top to bottom. Slice each half crosswise into four pieces (you should end up with 8 slices total) and set aside.
In a shallow baking dish or pie pan, whisk eggs, milk and cinnamon. Spray griddle or nonstick skillet with cooking spray and preheat to medium. Working in batches, dip panettone slices in egg mixture for 3-4 seconds per side. Shake off excess batter and place slices on griddle. Cook for 1 to 1 1/2 minutes per side, being careful not to burn chocolate chips (reduce heat if necessary). Serve immediately, with plenty of powdered sugar and maple syrup on the side. Dig in!