Prepare the Batter. In a large mixing bowl, combine the cornmeal, flour, baking powder, salt, pepper, diced onion, beaten egg, and milk. Stir until just combined, being careful not to overmix.
Heat the Oil. In a deep skillet or Dutch oven, heat the frying oil to 350°F over medium-high heat. Use a candy thermometer to monitor the oil temperature for best results.
Fry the Hush Puppies. Drop spoonfuls of the batter into the hot oil, working in batches to avoid overcrowding the skillet. Fry the hush puppies for 2-3 minutes per side, or until golden brown and cooked through.
Drain and Serve. Using a slotted spoon or spider strainer, transfer the fried hush puppies to a plate lined with paper towels to drain excess oil. Serve hot with your favorite dipping sauce or alongside your favorite Southern dishes.