Heat large nonstick pan to medium-high heat, and wipe a couple drops canola oil around surface.
Add dosa batter and tilt pan in circles to get batter to cover in thin layer. Then remove from heat and with fingers crush and spread boiled potatoes around batter, leaving a space in the middle.
Crack eggs in middle of dosa and place in 400°F oven for approximately five minutes or until eggs are set, but yolks are still runny.
Slide dosa onto a plate and dollop with chutney, drizzle with yogurt and a few radish slices, fresh mint leaves as garnish.
Put rice in bowl, rinse well and cover with 4 cups cold water.
Put urad dal and fenugreek seeds in small bowl; rinse well and add cold water to cover. Leave both to soak for 4 to 6 hours.
Drain rice and dal-fenugreek mixture in separate colanders. Put rice in a blender. Add one cup cold water and grind to smooth paste. It will take about 10 minutes and may be necessary to work in batches. Repeat process with dal-fenugreek mixture.
In a medium mixing bowl, combine the two pastes. Whisk together, adding enough water to obtain a medium-thick batter. You should have about 6 cups.
Cover bowl with kitchen towel and set in warm place. Let ferment until surface is bubbly, about 8 hours.
Stir in salt, set aside.