Colocasia leaves stir-fried with mustard oil — an everyday Assamese vegetable with earthy depth
Ingredients
- 4 large colocasia (taro) leaves
- 3 garlic cloves sliced
- 1 tbsp mustard oil
- 1 green chilli
- ½ tsp turmeric
- Salt
Method
About Kosu Xaak: Kosu Xaak uses the large umbrella-like leaves of the colocasia (taro) plant — a vegetable with a long history in Assamese cooking. The leaves have an earthy, slightly nutty character when properly cooked, and pair beautifully with the pungent mustard oil. Important: raw colocasia leaves contain irritant compounds that must be cooked out — proper preparation is essential.
Understand the plant: Colocasia (kosu in Assamese, arbi in Hindi, taro in English) is a tropical plant with very large heart-shaped or arrow-shaped leaves that can grow up to 50cm wide. The leaves are widely used in Assamese, Bengali and Manipuri cuisines.
The critical safety warning: Raw colocasia leaves contain calcium oxalate crystals that cause an extremely unpleasant itching sensation in the mouth and throat. Cooking destroys these crystals completely, but the leaves must be thoroughly cooked. Never taste raw colocasia leaves; always blanch them first.
Source fresh leaves: Use 4 large fresh colocasia leaves. They should be deep green, glossy, and feel firm. Yellowed or wilted leaves are old. Available at Indian groceries with a Northeast Indian or Bengali section, or at specialty Asian markets — taro plants grow widely in tropical Asia.
Wash thoroughly: Rinse the leaves under cold running water, gently rubbing the surfaces with your fingers to remove any soil or surface dust.
Remove the thick stems: The thick central stems of colocasia leaves are very fibrous and not pleasant to eat. Cut along both sides of the central stem to remove it. The thinner secondary veins can stay.
Chop the leaves: Stack the de-stemmed leaves and roll them like a cigar. Cut across the roll to produce thin chiffonade ribbons (1cm wide). This shape cooks evenly and looks elegant in the final dish.
The critical blanching step: Bring a large pot of water to a rolling boil. Add 1 tsp salt — the salt helps tenderise the leaves and starts to neutralise the calcium oxalate. Add the chopped leaves all at once.
Blanch for the full time: Boil hard for 3 minutes uncovered. The leaves will wilt down dramatically and turn a much deeper darker green. The 3-minute blanch is the minimum; you can blanch for up to 5 minutes if you are using particularly mature leaves.
Drain and squeeze: Drain in a colander. Rinse very briefly under cold water. Then take handfuls of the blanched leaves and squeeze hard between your palms to remove as much excess water as possible. Wet leaves will dilute the dish and the calcium oxalate compounds may not have fully drained out.
Double-blanch for extra safety (optional): Some Assamese cooks blanch a second time — for very mature leaves or for sensitive eaters, repeat the blanching process. Younger tender leaves rarely need a double blanch.
Prepare the garlic: Take 3 garlic cloves. Peel and slice thinly into rounds. Sliced rather than minced gives better visual appeal in the final dish.
Prepare the green chilli: Take 1 fresh green chilli. Slit lengthwise and chop into rounds.
Use a wide pan: Use a wide kadhai or large frying pan. The blanched leaves need space to stir-fry rather than steam.
Heat the mustard oil correctly: Pour 1 tbsp mustard oil into the pan over medium-high heat. Heat for 30-45 seconds until just smoking, to remove the raw bitter edge.
Fry the garlic: Reduce heat to medium. Add the sliced garlic. Stir for 30-45 seconds until lightly golden. Do not let it go dark.
Add the green chilli: Add the chopped green chilli. Stir for 15 seconds.
Add the blanched leaves: Add the squeezed-dry blanched leaves to the pan. Use a flat spatula to break up the squeezed clumps and spread evenly.
Add turmeric and salt: Sprinkle 1/2 tsp turmeric powder over the leaves. Add salt to taste — about 1/2 tsp. The leaves will turn a beautiful pale yellow-green.
The stir-fry: Stir-fry on medium heat for 4 minutes, turning the leaves with the spatula every minute. The leaves should fully integrate with the spices and turn a uniform colour. Any remaining moisture should evaporate, leaving the leaves coated in glossy oil.
Check the cooked texture: Taste a small piece. The leaves should be completely tender, with no residual scratchy feeling on your tongue (which would indicate undercooked oxalates). Soft, mildly nutty, gently spiced — that is the goal.
If any scratchy feeling: If you detect any tongue-scratching after tasting, return the pan to medium heat for 2-3 more minutes of cooking. Better safe than sorry.
Final taste: Adjust salt to your liking. The dish should taste earthy, mildly nutty, gently spiced, with the mustard oil providing aromatic depth.
Serve with rice: Serve hot alongside steamed rice — the most traditional Assamese pairing. The earthy leaves balance plain rice beautifully and provide a uniquely Assamese flavour. Pair with a piece of fish or a dal for a complete meal.
Variations: For a richer dish, add 1/4 cup grated coconut along with the blanched leaves — produces a coconut-flecked version popular in lower Assam. For protein, add 100g cubed firm tofu when adding the leaves — produces a vegetarian main dish.
Leftover storage: Stored in the fridge in an airtight container, kosu xaak keeps for 2-3 days. Reheat gently with a splash of water on the stovetop. The flavour deepens beautifully overnight as the leaves continue absorbing the mustard oil character.