Peel, core, and slice your apples into ½-inch to ¾-inch slices. Place them in a large bowl and pour over the milk. Toss to coat. Set aside.
In a pie plate or shallow dish for dredging, combine the flour, cornstarch, 1 tablespoon sugar, and 1 teaspoon cinnamon.
In a small bowl, combine 3 tablespoons sugar with ½ teaspoon cinnamon. Stir, then set aside.
Take about 6 to 8 apple slices out of the milk, let them drip off any excess milk, and place them into the flour mixture. Toss them gently to evenly coat on all sides. Place them on a large plate or tray, and repeat until all the apple slices are coated in the flour mixture.
Add ¼ cup of the vegetable oil to a medium-sized skillet that is set to medium heat. Place a paper towel-lined rimmed baking sheet, or large plate, next to your stovetop. This is where you will place your apple slices once fried to drain excess oil.
Fry 6 to 8 coated apple slices on each side for 1 to 1½ minutes per side, or until lightly golden. Transfer fried apple slices onto the paper towel-lined baking sheet. Sprinkle with the cinnamon-sugar mixture, then transfer to a serving plate.
Repeat until all apple slices are fried and sprinkled with the cinnamon-sugar mixture. See tip about adding fresh oil about halfway through the frying process.