Soak the chestnuts overnight in water. Drain and simmer in fresh water until tender (about 45-60 minutes).
When cool, cut chestnuts in half.
Cut each chicken thigh fillet into four pieces. Remove leaves from celery. Roughly chop and reserve a small handful of the leaves. Trim the ends and cut the stalks into long diagonal slices.
Heat a large wok on a high heat until just smoking. Add oil and when hot add the chicken pieces. After stir-frying for about a minute to seal the chicken, add spring onion, funghi and celery. Quickly fry together for about 30 seconds, then add the chilli bean paste and cook for about a minute until fragrant.
Reduce heat and add the sugar, soy sauce and stock. Bring to a simmer, add the chestnuts and simmer gently for about 3-5 minutes until sauce is lightly thickened. Add the sesame and chilli oils and check the seasoning.
Spoon into into a large, deep plate to share, garnish with the celery leaves and coriander sprigs and serve immediately.