Gather your large pan, sharp knife, and wooden spoon to prepare for cooking.
Pour the oil into the pan and heat over medium. Once shimmering, add the cumin seeds and toast until fragrant, about 30 seconds, releasing warm aroma.
Meanwhile, rinse the leeks thoroughly to remove grit, then slice them into thin half-moons. Add the sliced leeks to the pan.
Cook the leeks gently, stirring occasionally, until they soften and turn translucent, about 10 minutes. Their sweet aroma should fill the air.
Peel and dice the potatoes into 2-cm chunks. Add them to the pan with the leeks, stirring to coat the potatoes with the fragrant oil and spices.
Pour in the coconut milk, then add turmeric, ground coriander, and chili powder if using. Stir well to combine all the flavors.
Bring the mixture to a gentle simmer, then reduce the heat to low. Cover partially and cook for 20-25 minutes, stirring occasionally, until the potatoes are tender and the sauce is thickened.
Check the curry—potatoes should be soft and breaking apart slightly, and the leeks should be melting into a creamy sauce. Season with salt and pepper to taste.
Remove from heat and let sit for about 5 minutes to deepen the flavors. Give it a gentle stir before serving.
Spoon the warm, silky curry into bowls, garnishing with fresh herbs if desired. Serve alongside rice or crusty bread for a cozy, nourishing meal.
