Soak the grains: rinse and soak the Parboiled Rice, Raw Rice and the Urad Dal together for at least 4–6 hours; separately soak the Fenugreek Seeds with the Poha for 30 minutes. Cover with enough Water while soaking.
Grind and ferment the batter: drain the soaked rice mixture and grind it smooth with the fenugreek/poha mix, adding a little Water as needed to make a thick but pourable batter. Stir in about a teaspoon of Salt, cover, and leave in a warm place to ferment overnight or 8–12 hours until it rises and becomes slightly airy.
Prepare the potato masala: heat Oil in a pan, add Mustard Seeds and when they pop add a spoonful of Chana Dal and a little Urad Dal (if using), then toss in torn Curry Leaves. Sauté chopped Onion, sliced Green Chilies and grated Ginger until soft.
Add cubed boiled Potatoes to the pan, sprinkle Turmeric Powder and a pinch of Asafoetida, season with Salt and gently mash and mix so the potatoes absorb the spices. Finish with a splash of Lemon Juice and chopped Fresh Cilantro. Keep warm.
Make the coconut chutney: in a blender combine Grated Coconut, Roasted Chana Dal, a small piece of Ginger and chopped Green Chilies with a little Water and Salt to taste; grind to a smooth paste. Temper with a little Oil, frying Mustard Seeds, a split Dried Red Chili, a few Curry Leaves and a pinch of Asafoetida, then pour over the chutney.
Cook the sambar: rinse and pressure-cook Toor Dal with enough Water until soft; keep it slightly loose. In a pan sauté Small Onions/Shallots and chopped Tomato in Oil, add Turmeric Powder, Tamarind Pulp and Sambar Powder, then combine with the cooked dal and simmer to blend flavors. Adjust Salt and finish with chopped Fresh Cilantro. Temper with Mustard Seeds, Dried Red Chili, Curry Leaves and a pinch of Asafoetida.
Make the dosas: heat a nonstick or cast-iron griddle until very hot. Stir the fermented batter, pour a ladleful on the griddle and spread thin in a circular motion; drizzle a little Oil around the edges and cook until the underside is golden and crisp.
Assemble and serve: place a spoonful of the potato masala in the center of each dosa, fold or roll, and serve immediately with the coconut chutney and hot sambar for dipping.
