In a large bowl, whisk together the milk and egg. Add the corn, scallions, cheese, and apple cider vinegar and stir to combine. Sprinkle the salt, onion powder, baking powder, garlic powder, cayenne, smoked paprika, and several grinds of pepper over the mixture and stir again. Sprinkle on the cornmeal and flour and stir until well combined.

Coat the bottom of a cast-iron skillet with oil and heat over medium heat. Use a ¼-cup measuring cup to scoop the batter into the pan. Use the back of the measuring cup or a spatula to gently press down to flatten the fritters into about 3-inch disks. Cook for 2 to 3 minutes per side, or until golden brown and cooked through. Work in batches if necessary, wiping out the pan and adding more oil between batches.

Garnish with chopped scallions and serve with sour cream.