Stuffed chicken legs with mushrooms and cheese

Name: Stuffed chicken legs with mushrooms and cheese
Ingredients: 30g/1oz butter; 2 tbsp olive oil; 200g/7oz Portobello mushrooms, finely chopped; 1 large garlic clove, finely chopped; 75g/2¾oz cream cheese or mascarpone, beaten until soft; 75g/2¾oz Comté or other Alpine cheese, finely grated; small handful fresh flatleaf parsley, chopped; 1 tsp chopped fresh thyme leaves; 6 chicken legs (thigh and leg together), bone in and skin on; 250ml/9fl oz chicken stock; salt and freshly ground black pepper; mashed potatoes and cooked green beans, to serve