3 large shiitake mushrooms (2 ounces), stems discarded and caps cut into 1/2-inch dice
1/4 cup diced sweet onion
3/4 cup all-purpose flour
1 teaspoon baking powder
1 1/2 teaspoons kosher salt
1/2 teaspoon freshly ground pepper
Cut the corn kernels from the cobs and transfer half of them to a blender. Using the dull side of a knife, scrape the pulp from the cobs into the blender. Add the egg and milk; puree until smooth.
In a very large nonstick skillet, heat 1 tablespoon of the oil. Add the shiitake and onion and cook over high heat, stirring occasionally, until lightly browned, about 5 minutes. Add the remaining corn and cook, stirring, for 1 minute. Scrape the mixture onto a plate and freeze just until no longer hot, about 5 minutes.
In a bowl, whisk the flour, baking powder, salt and pepper. Stir in the puree, then fold in the corn kernels, shiitake and onion.
Wipe out the skillet and add the remaining 1/2 cup of oil. When it is hot, add eight level 1/4-cup mounds of batter to the skillet and spread them to a 1/2-inch thickness. Fry over moderately high heat, turning once, until the fritters are golden and crusty, about 4 minutes. Drain on paper towels and serve warm.