Dust the chicken with the flour. Heat the oil and butter in a large, wide pan with a lid, add the chicken, then fry on all sides until nicely browned. Add the shallots, then fry for about 2 mins until they start to soften, but not color. Pour in the brandy, carefully ignite, then stand well back until the flames have died down. Stir in the broth and bring to the boil. Reduce heat, cover, then cook for 15 mins until the chicken is just tender.
Add the asparagus to the sauce. Cover, then cook for 5 mins more until tender. Stir in the cream and tarragon and warm through. Season to taste.