Choose your substitute based on cooking method: shallots or pearl onions for roasting, yellow onion for braising, DIY blend or red onion for raw dishes.
Prep substitute as needed: peel and chop shallots and yellow onion, peel and measure pearl onions, finely dice white onion and scallion for the blend, or slice red onion thinly.
Apply recommended ratio: 1 medium shallot per cipollini, equal volume pearl onions or red onion, half weight yellow onion, and 3:1 white onion to scallion for blend.
Cook or use raw accordingly: roast or braise shallots, pearl, or yellow onions; use the blend or red onion raw in salads or salsas, rinsing red onion slices to reduce sharpness.
Adjust seasoning and texture by tasting and adding sugar with pearl onions if extra sweetness is needed.