01 - Preheat oven to 400°F.
02 - Heat olive oil in a large skillet over medium heat. Add chopped onion, diced carrots, and celery. Sauté for 6 to 8 minutes until softened.
03 - Add minced garlic and cook for 1 minute while stirring constantly.
04 - Stir in lentils, tomato paste, dried thyme, dried rosemary, smoked paprika, and bay leaf. Cook for 2 minutes.
05 - Pour in vegetable broth and soy sauce. Bring to a simmer, cover, and cook for 25 to 30 minutes, stirring occasionally, until lentils are tender and mixture thickens slightly.
06 - Remove bay leaf and stir in frozen peas. Season with salt and pepper. Simmer uncovered for 3 to 5 minutes until peas are heated through.
07 - Place peeled and chopped potatoes in a large pot of salted cold water. Bring to a boil and cook for 15 to 20 minutes until fork-tender.
08 - Drain potatoes and return to pot. Add plant-based milk, vegan butter, salt, white pepper, and nutritional yeast if using. Mash until smooth and fluffy.
09 - Spread lentil filling evenly in a 9 by 13 inch baking dish. Top with mashed potatoes, spreading to cover filling completely.
10 - Use a fork to create ridges on the mashed potato top for extra crispiness.
11 - Bake for 25 to 30 minutes, or until top is lightly golden and filling is bubbling at edges. For extra browning, broil for 2 to 3 minutes at the end.
12 - Let rest for 10 minutes before serving.