In a large mixing bowl, combine all-purpose flour, granulated sugar, cornmeal, baking powder, and salt. Whisk until well-blended and free of lumps.

Gradually pour in the milk into the dry mixture, stirring continuously until the batter is smooth and lump-free.

Carefully fold in the chopped onions, ensuring they are fully coated with the batter.

In a large skillet, heat enough vegetable oil over medium heat until it shimmers, about 5 minutes.

Drop heaping tablespoons of the batter into the hot oil and flatten slightly. Fry for 2-3 minutes, flip, and cook for another 2-3 minutes until golden brown.

Transfer the fritters onto a paper towel-lined plate to drain excess oil. Serve warm.