Lentil Shepherd's Pie with Root Vegetable Mash

Prepare the Root Vegetable Mash

1. Place the chopped potatoes and parsnips in a large pot and cover with salted water. Bring to a boil, then reduce heat and simmer for 15-20 minutes until both are completely fork-tender.
2. Drain the vegetables thoroughly. Mash them together until smooth, adding a tablespoon of olive oil and a splash of cooking water if needed to reach a creamy consistency. Season generously with salt and black pepper, then set aside.

Cook the Lentil Filling

3. Preheat your oven to 200°C (390°F).
4. Heat 1 tablespoon of olive oil in a large pan over medium heat. Add the chopped onion and sauté for 5 minutes until soft and translucent.
5. Stir in the tomato paste, dried thyme, and plain flour. Cook for 1 minute, stirring constantly, to toast the paste and flour.
6. Add the drained lentils, crumble in the vegetable stock cube, and pour in 250ml of water. Stir well to combine. Bring to a simmer and let bubble gently for 5-8 minutes until the gravy has thickened. Season with salt and pepper to taste.

Assemble and Bake

7. Transfer the rich lentil mixture into a medium-sized baking dish, spreading it into an even layer.
8. Spoon the potato and parsnip mash evenly over the lentils. Use a fork to smooth the top and create decorative ridges, which will catch the heat and crisp up.
9. Bake in the preheated oven for 20-25 minutes, or until the filling is bubbling at the edges and the mash topping is beautifully golden and crisp. Let it cool for 5 minutes before serving.