The day before

Cup of Yum
1. The day before you plan to have these, rinse the rice then leave it to soak in 1 ½cups/360ml of water. Rinse the lentils and fenugreek and cover them with water in a separate bowl. Leave both to soak for approx 3-4 hours.
2. After soaking, drain and rinse the rice then put it in a food processor or blender with ⅓cup/80ml water and grind until smooth. Transfer to a bowl then rinse the lentils and fenugreek and grind them until smooth with 1tbsp water as well. Mix the two together, cover with a cloth and leave for 8hours/ overnight to ferment. After it has fermented, if you don't need/want to use it straight away, you can store in the fridge, covered, for around 5 days. You may need to thin the mixture slightly before cooking.
3. Peel and dice the potatoes into bite-sized pieces and boil until tender. Drain and set aside (this can also be done ahead).

As you are ready to cook

1. Warm the oil in a skillet/frying pan and add the cumin and mustard seeds. Cook them a minute until they start to pop. Meanwhile, finely dice the onion then add it to the pan. Cook for approx 5min until starting to soften.
2. Add the garlic, ginger, turmeric and red pepper flakes. Stir and cook a minute then add the potatoes. Cook for another minute or two, adding a little more oil if needed if it's sticking, then set aside.
3. To cook the dosas, warm a little oil in a medium-large skillet or griddle and ensure the oil covers the pan. Drop approx ¼cup/60ml of the mixture into the pan and quickly spread it out into a thin layer with the back of a spoon/ladle - it's often easier in a circular motion - trying to avoid having thick areas. Cook until the dosa is starting to brown around the edges.
4. Loosen the dosa with a spatula from the bottom of the pan and spoon a couple spoonfuls of the potato mixture in the middle of the dosa, fold in the sides and warm a minute then serve. Repeat with the remaining mixture.