Bring a large pot of water to boil on the stove. While waiting for the water to boil, blend together the butter, fresh cilantro, and cumin in a bowl or food processor. Add the lime juice and mix until incorporated; set aside. Place corn in boiling water, and cook for 3 to 5 minutes until kernels are bright yellow and just tender. Remove from the heat and drain.

Spread the seasoned butter on hot corn, dust with chili powder and salt if desired, and serve immediately. Wrap any leftover butter in plastic wrap or waxed paper.