Chicken and leek casserole with tarragon dumplings

Name: Chicken and leek casserole with tarragon dumplings
Prep time: 15 min
Cook time: 1 h 40 min
Total time: 1 h 55 min
Cuisine: British
Ingredients: 18.40 gm vegetable oil; 800g chicken thigh fillets, coarsely chopped; 50g butter; 200g button mushrooms, halved; 2 large leeks, pale section only, thickly sliced, washed, dried; 2 garlic cloves, crushed; 40.00 ml plain flour; 500ml (2 cups) chicken style liquid stock; 60ml (1/4 cup) fresh lemon juice; 60ml (1/4 cup) thin cream; Salt & freshly ground black pepper; 1 x quantity tarragon & mustard dumplings variation (see notes)