In a mixing bowl, whisk together flour, sugar, and salt.
Add eggs, milk, and melted butter. Whisk until smooth.
Heat a non-stick skillet over medium heat. Pour ¼ cup of batter into the skillet, tilting to cover the bottom. Cook until edges are dry, then flip and cook the other side. Repeat with remaining batter.
In another skillet, melt butter for the filling. Add apples, brown sugar, and cinnamon. Cook until apples are tender.
Fill each crepe with apple mixture, fold, and serve warm.