1. Prepare the mash

Bring a large pot of salted water to the boil. Add the sweet potatoes and regular potatoes and cook until very tender, about 20 minutes.

Drain well and return to the warm pan. Add the butter, milk, Herbes de Provence, salt, and pepper. Mash until smooth and creamy. Set aside.

2. Build the filling

Heat the olive oil in a large sauté pan or Dutch oven over medium heat.

Add the onion and cook gently for 8–10 minutes until soft and lightly golden.

Add the celery, carrots, mushrooms, and garlic. Cook for another 8 minutes, stirring occasionally, until the mushrooms have released their moisture and the vegetables begin to caramelize.

Stir in the tomato paste and cook for 2 minutes.

Add the cumin, Herbes de Provence, rosemary, thyme, bay leaf, and black pepper.

Pour in the wine and allow it to simmer for 2–3 minutes.

Add the lentils, crushed tomatoes, tamari, and vegetable broth if needed. Simmer gently for about 20 minutes until thick and rich.

Stir in the peas, balsamic vinegar, and chopped parsley.

Mix the cornstarch with the water to make a smooth slurry. Stir it into the filling and cook for another 2–3 minutes until glossy and thickened.

Remove the bay leaf.

3. Assemble

Heat the oven to 400°F (200°C).

Spoon the lentil filling into a large baking dish.

Spread the sweet potato mash evenly over the top, creating soft peaks with the back of a spoon. These little ridges become beautifully golden in the oven.

4. Bake

Bake for 25–30 minutes until bubbling around the edges and lightly golden on top.

Allow the pie to rest for 10 minutes before serving.

Finish with chopped parsley, a few rosemary leaves, and, if you like, a drizzle of extra virgin olive oil.