1. Peel, rinse, and dry the potatoes. Cut them into large cubes. Place them in a saucepan and cover with cold water. Cook for 10 minutes: the potatoes should still be slightly firm. Drain them.
2. Peel and finely chop the onion. Drain the tomatoes over a container. Reserve the juice and dice the tomatoes. Heat the oil in a sauté pan, add the onion, curry, and chili, and mix for 30 seconds over low heat. Then add 6 tablespoons of water. Cover and cook over low heat for 4 minutes, stirring occasionally.
3. Add the still frozen spinach, mix, and cook over low heat for 10 minutes, without a lid. Season with salt during cooking. Blend the mixture, return it to the pan over low heat, and add the potatoes, diced tomatoes, and their juice. Simmer for 10 minutes until the sauce is creamy. Stir frequently during cooking.