Whisk eggs and salt together in a bowl. Gradually stir flour into eggs, alternately with 2 cups milk until fully incorporated. Beat 1/4 cup vegetable oil and 1/2 teaspoon cinnamon into flour mixture. Refrigerate batter for at least 1 hour.
Mix apples, sugar, 2 teaspoons cinnamon, and 2 tablespoons water in a pot.
Whisk cornstarch and 1 tablespoon water in a small bowl; pour into apple mixture.
Simmer apple mixture over medium heat, stirring often, until thickened, 8 to 10 minutes. Keep warm.
Whisk 1 1/2 tablespoons milk into chilled batter.
Heat about 1 teaspoon vegetable oil in a crepe or frying pan over medium heat.
Pour about 1/3 cup batter into the heated oil; tip and rotate the crepe pan until the batter covers the entire area. Cook until the edges begin to curl away from the sides of the pan, about 30 seconds; flip the crepe and continue cooking until lightly golden on the other side, about 30 more seconds.
Remove crepe from pan, add more oil, and repeat with remaining batter.
Spoon the apple filling into each crepe; fold crepe over the filling and serve.
