Heat 1 tablespoon of the oil in a frying pan. Add garlic. Cook over medium heat until soft. Remove and set aside.
Dust eggplant slices with flour and season. Heat 2 tablespoons of remaining oil in same hot pan. Add half the eggplant slices. Cook for about 5 minutes on each side or until golden brown and tender. Remove and drain on absorbent paper. Repeat with 2 tablespoons oil and remaining eggplant.
Divide eggplant among four ovenproof ramekins (1¾ cup capacity). Top with prawns and jamon.
Heat remaining oil in a medium saucepan. Add onion. Cook, stirring occasionally, until soft and golden brown. Add flour. Cook, stirring, for 1 minute. Gradually whisk in milk and stock. Cook, whisking, until smooth and thickened. Season. Strain.
Divide sauce among ramekins. Sprinkle with cheese. Place ramekins on an oven tray. Cook in the oven for about 20 minutes or until prawns are cooked and cheese is golden.