Preheat oven to 375 degrees F. Grease six 6-ounce ramekins or custard cups; set aside. In a covered medium saucepan, cook fresh corn and onion in a small amount of boiling lightly salted water for 6 minutes. (Or cook frozen corn and onion according to package directions for corn.) Drain well.
In a medium bowl, lightly beat eggs with a fork. Stir in drained corn and onion, evaporated milk, garlic salt, and pepper. Stir in 3/4 cup of the cheese. Pour into prepared ramekins. Place filled ramekins in a 15x10x1-inch baking pan.
Sprinkle remaining 1/4 cup cheese over corn mixture. Bake, uncovered, for 30 minutes. Let stand for 10 minutes before serving. Makes 6 side-dish servings.