Thinly slice the onion and transfer it to your preferred glass container.
Add the peppercorns and set aside.
In a small pot, add the balsamic vinegar, water, maple syrup, herbs, and salt.
Stir well and bring to a simmer. Then, remove from the heat.
Pour the steamy hot vinegar mixture over the onions and seal the jar.
Shake the jar a few times and let it cool down on the counter for about one hour before placing it in the fridge.