Preheat the oven to 180°C. Grease an ovenproof dish (that can also be frozen) with non-stick spray. Line a baking sheet with foil and grease with non-stick spray.
1. White sauce: Melt the butter in a saucepan. Add the flour and stir until smooth and the mixture starts simmering. Then slowly add the milk, stirring continually, until it starts boiling. Season with salt and pepper and stir in half the cheese.
2. To finish: Slice the brinjals in long, thin strips. Sprinkle salt over and leave to stand for 15 minutes. Rinse and pat dry with paper towels.