Break the egg into a 2-quart or larger bowl and beat it lightly with a fork to break it up. Add the corn kernels, cornbread mix, Cheddar and cottage cheeses, and milk and stir well to mix.

Spray a 12-inch nonstick skillet with cooking oil spray and heat over medium heat. Drop the batter, one fourth at a time, into the skillet, to make 4 fritters. Flatten the mounds of batter lightly with the back of a spoon.

Fry the fritters until lightly browned, 2-1/2 minutes per side. Serve at once, with salsa (if using) on the side.