Chicken and Mushroom Pie with Duchess Potato Topping

Reduce the heat to medium and add the remaining butter. Once melted, sprinkle in the flour and stir for 1 minute to form a roux. Gradually whisk in the beef stock and water until smooth, then stir in the tomato paste, remaining salt, and black pepper.

Return the mushrooms and their juices to the pan. Simmer for about 10 minutes, or until the sauce thickens into a rich gravy and the mushrooms are tender. Add the chicken and simmer for 2 to 3 minutes more, until the chicken is just cooked through and the filling is thick enough to hold its shape.

Preheat the oven to 200°C / 390°F (180°C fan). Mash or rice the cooked potatoes until smooth, then stir in the milk, a little butter, and the white pepper. Season with salt and mix until creamy but still firm enough to pipe or spoon.

Spoon the chicken filling into a 1.5 to 2 liter baking dish and smooth the top. Pipe or spoon the mashed potatoes over the filling in swirls or small mounds, then sprinkle with the Parmesan.

Bake for 30 minutes, rotating the dish once if needed, until the topping is lightly golden and the filling is bubbling around the edges. Rest for 10 minutes before serving, then finish with chopped parsley.