Pre-heat your oven to 180C / 356F / gas mark 4.

In a sauce pan, melt the butter in the olive oil on a low heat before adding the sliced leek and the salt then cook for 2-3 minutes.

Add the diced carrot and cauliflower then cook for another 5-8 minutes until the carrots, cauliflower and leeks have started to soften.

Add the mushrooms and crushed garlic to the pan and cook for another 5 minutes.

In a separate pan, melt another tablespoon of butter and add the plain flour. Stir until the butter has created a paste with the flour.

Pour in the milk and mix well so that the flour dissolves in the milk creating a thick sauce.

Let the sauce simmer gently before adding the cheese, nutritional yeast, black pepper and mustard.

Once the cheese has melted add in the frozen peas and pour over the rest of the vegetables.

Cook until the peas have thawed and the cheese sauce has thickened.

While the vegetables are cooking in the sauce, roll out your pastry and cut out a lid, exactly the same size as the top of your oven dish.

Spoon the cheesy vegetable mix into your pie dish.

Place the pastry lid on top of the vegetables and press the edges down using a fork.

Place into the centre of your oven and cook for 45 minutes or until the pastry is crisp and golden brown.