1 bunch young asparagus, about 10 spears, trimmed
1 medium onion, finely sliced
freshly ground black pepper
25g/1oz cornflour
1 tsp olive oil
flaked sea salt
1 tbsp sunflower oil, plus extra for oiling the tin
25g/1oz extra-mature Cheddar cheese, finely grated
3 free-range eggs, beaten
4 sheets filo pastry, each about 32 x 38cm/13 x 15in
300ml/陆 pint semi-skimmed milk
5 rashers dry-cure smoked back bacon