Place a medium saucepan over medium-high heat and add enough water to completely cover the duck eggs once added.
Allow the water to come to a rolling boil, then use kitchen tongs to carefully lower each duck egg into the bubbling water to prevent cracking from impact.
Reduce the heat to medium-low to maintain a gentle simmer and cook the eggs for exactly 30 minutes - this ensures the embryo is fully cooked while keeping the texture tender.
While the eggs cook, combine the finely chopped onion with cane vinegar in a small bowl and set aside to let the flavors meld.
After 30 minutes, use tongs to carefully remove the hot eggs from the water and place them on a clean surface to cool until they're comfortable to handle.
Hold the cooled egg upright and gently crack the top, being careful not to damage the contents inside.
Pour the clear liquid from the top of the egg into your vinegar and onion mixture - this adds extra flavor to your dipping sauce.
Carefully peel away the remaining shell to reveal the balut inside, then place it in the bowl with your prepared sauce.
Season with salt and freshly ground black pepper according to your taste preference.
Serve immediately while still warm for the best texture and flavor experience.