Wash 80 g split urad dal to remove any debris or stones. Once washed, add them to a deep bowl with around 200 ml water. Cover the bowl and set aside to soak for a minimum of four hours.
After soaking, drain the soaked urad dal of any excess water (most should have been absorbed). Add to a mixer grinder along with 1 tablespoon cold water, and make a smooth paste. You can test if the batter has been ground enough by dropping a small piece in cold water — it should float.
Heat 1 litre neutral oil in a large, deep kadai, saucepan, or deep fat fryer over medium-high heat.
While the oil heats, add the spices to the batter. Transfer the batter to a bowl and add coarsely ground black pepper (to taste), 2 strands fresh coriander (finely chopped), 10 g onion (finely chopped), ¼ teaspoon cumin seeds, 1 green chilli (finely chopped), and sea salt to taste. This step is quite forgiving; you can also add ginger and curry leaves, which are traditional, or vary the quantities. Lightly fold through the batter.
Once the oil is hot enough (you can test this by dropping some batter — it should rise quickly but not brown immediately), start shaping the medu vada*. Take a small bowl of cold water. Wet your hands and with your dominant hand, take a small portion of the batter. Use your fingers to flatten and smooth the top of the vada. Then, use your thumb to make a large hole in the middle. Once done, carefully slide the vada into the hot oil. Repeat.
Fry the medu vada for around 5 minutes or until a deep golden brown. Drain excess oil on a kitchen towel and then serve hot with chutney or sambar.
Notes
* You can also buy a batter dispenser if you don't want to hand-shape the medu vada.