In a saucepan, combine the rinsed lentils and vegetable broth. Bring to a boil, then reduce to a simmer and cook for about 20-25 minutes, or until lentils are tender. Drain any excess broth if necessary.

In a large skillet, heat a little olive oil over medium heat. Add diced onions, carrots, and celery and sauté for about 5-7 minutes until softened. Add in the minced garlic and cook for an additional minute.

Stir in the cooked lentils, tomato paste, dried thyme, paprika, salt, and pepper. Cook for a few more minutes until the mixture is heated through.

In a pot, boil the peeled and cubed potatoes until tender, about 15-20 minutes. Drain and mash them with milk and butter until smooth and creamy. Add salt and pepper to taste.

Preheat your oven to 400°F (200°C). In a baking dish, spread the lentil and vegetable mixture evenly, and top with the creamy mashed potatoes. Use a fork to create texture on top, which will become golden when baked.

Place the assembled pie in the oven and bake for about 25-30 minutes, or until the top is golden brown.

Allow the pie to cool for a few minutes before serving. Enjoy!