Ingredients :

• Red onions — Choose the firmest ones, those that resist when you squeeze slightly. A soft onion has already surrendered — it will soften too quickly and won’t caramelize properly. Ideal size: medium. Not too big (layers are thick, cooking is uneven), nor too small (you’ll spend all your time peeling).
• Olive oil — No need to pull out the overpriced bottle. Ordinary olive oil does the job perfectly here — heat destroys fine aromas anyway. What matters is the quantity: enough to coat the entire bottom of the pan, no more. Too little and it sticks. Too much and it slides, and nothing browns.
• Salt — Salt isn’t primarily there for seasoning — it’s there to draw the water out of the onions. This water then evaporates, triggering the caramelization. Add it right at the start with the onions, not at the end.
• Lemon juice or balsamic vinegar — Optional on paper, indispensable in practice. The acidity at the very end of cooking cuts through the sweetness of the onions and wakes everything up. Lemon provides lightness and freshness. Balsamic adds a darker, slightly syrupy depth. Choose based on what you are serving the dish with.