3 celery sticks, trimmed and finely chopped
6 garlic cloves, finely grated
2 leeks, trimmed and chopped
small handful of chopped fresh tarragon
600ml/20fl oz chicken stock
50²µ/1¾´Ç³ú plain flour, plus extra for dusting
salt and freshly ground black pepper
1 tbsp olive oil
50²µ/1¾´Ç³ú butter
4 heaped tbsp crème fraîche
1 free-range egg, beaten, for glazing
500g/1lb 2oz ready-made shortcrust pastry
12 chicken thighs (approximately 900g/2lb untrimmed weight), boneless, skinless, fat trimmed and cut into bite-sized pieces
200g/7oz pancetta, chopped into small cubes