Mix half the oil and flour in a saucepan (off
the heat), then blend in the soya milk (it must
be well blended before heating). Bring the
sauce slowly to the boil, whisking constantly,
then simmer for 1 min. Remove from the heat,
cover with greaseproof paper and set aside.
Heat oven to 200C/fan 180C/gas 6. Heat
remaining oil in a frying pan, add the chicken,
then fry for 2-3 mins or until brown (it won’t
be cooked through). Transfer to an ovenproof
gratin dish. Add the onions to the pan and fry
for 2-3 mins. Spoon over the chicken, then
top with the tomatoes and asparagus. Set
aside while you prepare the sauce.
Put the sugar and vinegar into the pan.
Stir over medium heat until the sugar is a dark
caramel colour, then add the stock. Bring to
the boil and simmer for 1 min. Whisk into the
milky sauce until blended, season, then add
the tarragon. Spoon sauce over the chicken
and veg, sprinkle with crumbs and cheese,
then bake for 20 mins or until cooked through.