Rinse the lentils under cold water and set aside. Bring the vegetable broth to a boil in a large saucepan, then add the lentils. Reduce the heat to a simmer (~90°C / 194°F) and cook for 25-30 minutes until tender but not mushy. Drain any excess liquid and set the lentils aside.
Peel and dice the carrots and onion. In a skillet over medium heat (~160°C / 320°F), add a splash of olive oil and sauté the diced vegetables for about 8 minutes until fragrant and slightly caramelized, with the onions becoming translucent and the carrots softening.
Stir in the tomato paste and cook for 1-2 minutes, allowing it to deepen in color and aroma. Add the cooked lentils, thyme, rosemary, and a splash of vegan Worcestershire sauce. Pour in 1 cup of vegetable broth, then simmer uncovered for 10 minutes until the mixture thickens and flavors meld. Taste and season with salt and pepper as needed.
While the filling simmers, peel the potatoes and cut them into even chunks. Boil them in salted water (~100°C / 212°F) for 15-20 minutes until very tender when pierced with a fork. Drain well and return to the hot pot to steam-dry for a minute or two.
Mash the hot potatoes with olive oil or vegan margarine until smooth and fluffy. Season with salt and pepper to taste. Keep warm.
Preheat your oven to 200°C (392°F). Spread the lentil filling evenly in your baking dish. Dollop the mashed potatoes on top and spread evenly with a spatula or spoon, creating a rustic textured surface.
Bake uncovered for 20-25 minutes until the top is golden brown and bubbling around the edges. For extra crispness, broil on high for 2-3 minutes, watching carefully to prevent burning.
Remove from the oven and let the shepherd’s pie rest for 5-10 minutes. This helps the filling set and makes slicing easier. Serve warm, garnished with herbs if desired.
