Peel and core the apples, then slice them into 1/4-inch rings.
In a bowl, whisk together the flour, sugar, cinnamon, baking powder, and salt.
In a separate bowl, beat the egg, then mix in the milk and vanilla extract.
Gradually add the wet ingredients to the dry ingredients, stirring until smooth.
Heat vegetable oil in a deep pan to 350°F (175°C).
Dip each apple ring into the batter, allowing excess to drip off.
Carefully fry the apple rings in batches until golden brown, about 2 minutes per side.
Remove from oil and drain on paper towels.
Dust with powdered sugar and serve warm.