pre heat oven to 160 degrees
Heat stock in saucepan
heat oil in heavy based pan,
Add sliced leek and rice stir until rice is well coated in oil.
Add garlic stir for 1 minute.
Add white wine, stir until absorbed by rice (about 2 mins)
Add thinly sliced chicken
Add 3/4 of the heated stock, stir and bring to the boil
Transfer to casserole dish, place in oven for 1/2 an hour, stirring every 15mns
Add mushrooms and remaining stock,
Place back in oven for 30 mins, stirring after 15 mins
Serve