Using a fork, prick potatoes and place into a bowl.
Coat potatoes with oil and salt and place onto a baking tray. Bake potatoes in the oven at 220°C for an hour or until potatoes are soft inside.
Meanwhile: Heat oil in a large pan over a medium heat. Add onions and garlic and cook until the onions start to soften (3-4 minutes)
Stir in the carrots and celery and cook for a further 5 minutes until softened.
Add in the chopped mushrooms, dried thyme, salt and paprika and cook gently until most of the juices have been released from the mushrooms. (5 minutes)
Spoon in the tomato puree and flour and stir until the vegetables are coated. Cook until the flour coats the bottom of the pan.
Pour over the puy lentils and stir in red wine and 2/3rds or the vegetable stock.
Cover pan with lid and let simmer for 30 minutes or until the lentils are tender, stirring occasionally. Add more vegetable stock when needed
When potatoes are cool enough to handle, using a serrated knife cut a lid out the top of the potato. Scoop out the potato and place into a bowl.
Add milk and butter to potato and mash together with a fork until smooth. Spoon into a piping bag with a star tip (optional)
Spoon sheppard pie filling into the potato skins making sure to pack it down. Pipe over the mash potato and place into the oven for 15-20 minutes.
Sprinkle over cheese and cook until melted (optional)