Assemble the jar: Add the sliced onions, garlic, herbs, spices, and your sweetener of choice (maple syrup or honey) to a glass jar.
Add the brine: Pour in equal parts vinegar and water until the onions are fully submerged. Secure the lid and shake well to combine.
Chill: Refrigerate for at least 1 hour before using. The flavor gets even better as they sit.
Notes
This is a very no recipe, recipe. The onion sizes will vary as will the size of glass jar you can use. The main thing to remember is equal parts vinegar and water and make sure your onions are completely covered in the liquid. After that, the sky is the limit as far as how you can flavor them!