Leek (Best Option)
1/2 cup chopped leek per 1/2 cup chopped onionLeeks belong to the same allium family as onions and share many of the same sulfur-containing compounds responsible for the characteristic onion flavor. Their mildness means they impart a subtle sweetness and aromatic depth without overpowering the chili.
When using leeks, clean them thoroughly to remove grit, and use the white and light green parts for the best texture. Because they are milder, you may want to slightly increase the quantity or cook them a bit longer to develop flavor fully.
The final chili will have a slightly sweeter and less sharp onion note, which can enhance the overall balance of the dish, especially in recipes with longer simmering times.