One-pan Bistro Chicken with Creamy Mushrooms and Prosciutto (gf)

1 tablespoon each olive oil and butter
2 whole chicken legs (thigh and drumstick)
sea salt and ground pepper
1 medium brown onion, finely chopped
2 bay leaves
2 cloves garlic, crushed
2 teaspoons dried tarragon
250 grams small portobello mushrooms
3 tablespoons brandy
1 cup chicken stock
1 tablespoon wholegrain mustard
½ cup cream
4-6 slices prosciutto

Preheat the oven to 160°C fan bake.

Heat the oil and