In medium sized mixing bowl, combine cornmeal mix, flour, corn muffin mix (if using) sugar (if using), eggs, chopped onions (if using), and buttermilk.
NOTE: Use 2 small or medium eggs. Or use ONE large egg.
Stir together until evenly combined and smooth. Set aside.
Pour 3 tablespoons of vegetable oil into an 8" or 9" skillet. Slowly warm over low-medium heat until oil is sizzling hot (not smoking).
Again, stir cornbread batter until smooth. Pour 1/4 cup into skillet with hot oil. This will create one flapjack. Looks like a pancake.
Cook over low-medium heat until edges look dry and bubbles form on top (about 3 minutes).
Flip over. Cook another 3 minutes or until golden brown.
After the 3rd flapjack, add more vegetable oil to skillet.
Pour in batter and fry. Repeat until all batter is fried.
Drain on paper towels. Serve hot.