Put pasta shells on to cook in plenty of salted boiling water. Cut skinless boneless chicken thighs into bite-sized chunks,
dust lightly in seasoned flour and fry in hot olive oil until cooked and browned. Scoop out and set aside. Add a knob of butter
to the pan and fry sliced mushrooms until they are nicely browned, seasoning with freshly ground black pepper. Scoop these out
and put with the chicken. Fry a chopped shallot and a crushed clove of garlic until softened, then return the chicken and mushrooms
to the pan. Tip in 3 – 4 Tbs crème fraiche together with a good splash of the pasta cooking water and bring to a simmer. Stir in
chopped tarragon, cover and simmer gently for 5 – 6 minutes, until the sauce thickens and the chicken is cooked. Stir in the cooked
and drained pasta and serve in warm bowls.