Step 1

To make the dosa batter, place rice in a sieve and rinse under cold running water. Transfer half the rice to a saucepan of boiling water and cook for 5 minutes to par-cook. Drain and rinse again. Combine par-cooked and uncooked rice in a large bowl and pour in enough cold water to cover by 5cm. Loosely cover and set aside for 12 hours to soak. Meanwhile, place urad dal in a sieve and rinse under cold running water. Place in a separate bowl with fenugreek seeds. Pour in enough cold water to cover by 5cm, then loosely cover and set aside for 12 hours to soak.

Step 2

Whiz rice and 100ml rice soaking liquid in a food processor for 10 minutes or until a smooth but slightly grainy paste. Transfer to a large bowl. Place urad dal, fenugreek seeds, 100ml urad dal soaking liquid and 11/2 tsp salt in a food processor and whiz until a light creamy paste. Add enough water, 1 tbs at a time, to loosen to a batter. Add ground urad dal mixture to ground rice, then loosely cover and set aside in a warm place for 12 hours to ferment; it should increase slightly in volume and be foamy and creamy. If too thick, add enough water to form a pourable batter. If not cooking dosas immediately, chill batter until needed, then bring to room temperature before cooking.

Step 3

For the potato filling, when ready to cook dosa, place potatoes in a large saucepan of salted water and bring to the boil over medium-high heat. Cook for 20-25 minutes until just tender. Drain and cool slightly, then cut into 2cm pieces. Place garlic, ginger and chilli in a small bowl and stir to form a paste. Heat the oil in a large frypan over medium heat. Add mustard and cumin seeds, and cook for 1 minute or until fragrant. Add onion and curry leaves, and cook for 3-4 minutes until onion is softened and curry leaves are crisp. Add garlic, cook for 2 minutes, then add turmeric, spinach and chopped potato, and cook, stirring, for 2-3 minutes until coated and yellow. Stir in most of the coriander and remove from heat. Cover with a lid to keep warm.

Step 4

Place a large frypan over medium-high heat. Brush pan with 1 tsp oil. Ladle in 1/2 cup batter or just enough to form a thin pancake, spreading out with bottom of ladle. Drizzle over a little oil and cook for 5-6 minutes until base is crisp (you only need to cook one side). Slide dosa onto a plate, then spoon in potato filling and fold over or roll up. Repeat with remaining batter and filling. Serve with chutney and remaining coriander leaves.