Recipe Card

Place the onions in a jar; fill the jar about a third of the way with vinegar, then fill to the top of the onions with water. Add salt and sugar, shake, and keep in the fridge for a few hours or a few days. (Suggest 30 minutes minimum if short on time.)
Shake all dressing ingredients in a jar. Adjust to taste and keep in the fridge if making ahead.
Chop the romaine and herbs, and gently tear the butter lettuce into bite-sized pieces.
Just before serving, toss greens, herbs, pickled onions, and dressing together, starting with about half of the dressing and adding more as necessary. Adjust seasoning to taste.