Peel and thinly slice the onion and lemons into 1/8 inch pieces.
Layer a third of the onion slices at the bottom of a clean mason jar, followed by a third of the lemon slices.
Drizzle 1/4 cup raw honey over the first layer, pressing gently to remove air pockets.
Repeat the layering process until all ingredients are in the jar, topping with the last portion of honey.
Optionally add apple cider vinegar or essential oils at this stage.
Cover with parchment paper and seal with the jar lid, then store in a cool, dark place for 24–48 hours.
After infusion, strain the syrup through a fine mesh sieve into a clean glass bottle, pressing the solids gently to extract all liquid.
Store the syrup in the refrigerator for up to 1 month or freeze for up to 9 months.
Shake before each use, and take 1 tablespoon for adults or 1 teaspoon for children over 1 year as needed.