Step 1Combine the chile, cumin seeds, ginger, curry leaves, cilantro and water in a small food processor or spice grinder and process to a paste. Set aside.
Step 1Combine the milk and half-and-half in a 2-cup measure or small bowl. Combine the oil, cumin and mustard seeds, if using, in a large saucepan over medium-high heat. Cover, if using mustard seeds, and cook until the cumin turns golden brown or you hear the mustard seeds crackle, 1 to 2 minutes.
Step 2Add the chiles, turmeric, curry leaves and asafetida (if using) and stir. (Stand back when adding the curry leaves. They spit when they hit the oil.) Immediately add the green paste and reduce the heat to low. Then cook, stirring, 1 minute.
Step 3Add the flour and cook, stirring, 1 more minute, scraping the bottom of the pan to keep the flour from sticking. Gradually add the milk mixture, about 1 tablespoon at a time at first, to make a smooth paste. Start to add the milk more quickly, adding the final cup all at once.
Step 4Stir in the salt and the corn and bring to a boil. Reduce the heat and simmer, covered, until the corn is tender, about 4 minutes. Taste for salt and serve hot.