In a blender or food processor, process the flour, salt, egg yolks, butter and cider. Process until smooth.
In a large bowl, beat the egg whites.
Fold the flour mixture into the beaten egg whites, just until combined.
Peel and core the apples; cut into 1/4 inch thick slices.
Sprinkle the apple slices with lemon juice and toss with the sugar.
Heat 4 to 5 inches of oil in a large and heavy-duty saucepan over med.-high heat until the oil is hot enough to sizzle when a tiny bit of batter is dropped inches.
Dip an apple slice in batter - it should be evenly coated with batter, allowing excess batter to drip off. Repeat with several more apple slices.
Carefully drop battered apple slices into the hot oil. Cook 8 to 10 minutes or until the apple slices are cooked through and the batter is puffy and golden. *Work in batches so you don't overcrowd the pan*.
Drain on paper towels.
Repeat until all apple slices are battered and cooked. Let cool., then sprinkle with powdered sugar before serving.