Chicken stew with cider and chorizo

Name: Chicken stew with cider and chorizo
Ingredients: 2 tbsp olive oil; 4 whole chicken legs (drumstick and thigh separated); 225g/8oz chorizo, diced; 6 shallots, peeled, finely chopped; 2 tbsp plain flour; 600ml/1 pint dry cider; 150ml/¼ pint chicken stock; 1 heaped tbsp Dijon mustard; salt and freshly ground black pepper; 3 tbsp double cream; 1 celeriac, peeled, chopped; squeeze fresh lemon juice; 25g/1oz butter; 1-2 tbsp single cream; salt and freshly ground white pepper; steamed green beans, to serve