Pre-heat the BBQ for 1-2 minutes with the Paella Pan in place and add a drizzle of oil and a little butter. Gently sauté the onions for 2-3 minutes before adding the leeks and cook for 5 minutes more on a low heat.

Add the mushrooms and fresh herbs, stir and cook, covered for 5-6 minutes. Once the mushrooms have softened and released their water, remove the lid, turn the heat to medium and add some salt and pepper. Cook until the mushrooms take on a golden colour and all the liquid has evaporated. Tip into a bowl and set aside.

Make your sauce by adding the butter to the Paella Pan and once melted, stir in the flour. Cook for a minute on a low heat then slowly whisk in the combined milk and stock a little at a time, stirring constantly. Continue this way until you have a nice thick sauce. Stir in the mustard along with the wine and let it bubble away gently for 10 minutes, then add the cheese.

Add the mushroom mixture to the pan and stir well to combine everything together. Set aside to cool slightly.

Dust your work surface with flour and roll out the pastry to the size of the pan. Lay across the top of the pie filling so the surface is covered. Brush with a little beaten egg. Bake with the lid on the BBQ for around 30 minutes until golden and crisp.