Preparation – Getting Started (Approx. 20 minutes):

1. Preheat Oven and Prepare Baking Dish: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch (or similar sized) baking dish. This will prevent sticking and ensure even baking.
2. Prepare Vegetables: Wash, peel, and chop all your vegetables according to the ingredient list. Dice the onion, carrots, and celery into roughly similar-sized pieces. Slice the mushrooms. Mince the garlic. Having all your vegetables prepped and ready to go will make the cooking process much smoother and faster.
3. Prepare Potatoes for Topping: Peel and quarter the potatoes. Place them in a large pot and cover them with cold water. Add a generous pinch of salt to the water. Bring the pot to a boil over high heat and cook until the potatoes are fork-tender, about 15-20 minutes. Boiling in salted water seasons the potatoes from the inside out and ensures they cook evenly. While the potatoes are boiling, you can proceed with making the vegetable filling.

Making the Vegetable Filling (Approx. 30-40 minutes):

1. Sauté Aromatics: Heat the olive oil in a large, deep skillet or Dutch oven over medium heat. Add the chopped onion, carrots, and celery. Sauté for 8-10 minutes, or until the vegetables begin to soften and the onions become translucent. Stir occasionally to prevent sticking and ensure even cooking. Sautéing these vegetables first builds a flavorful base for the entire dish.
2. Add Mushrooms and Garlic: Add the sliced mushrooms to the skillet and cook for another 5-7 minutes, or until the mushrooms release their moisture and begin to brown slightly. Stir occasionally. Then, add the minced garlic and cook for 1 minute more, until fragrant. Be careful not to burn the garlic, as it can become bitter.
3. Build Flavor Base: Stir in the tomato paste, dried thyme, and dried rosemary. Cook for 1-2 minutes, stirring constantly, until the tomato paste darkens slightly and the spices become fragrant. This step, known as “blooming” the spices and tomato paste, enhances their flavors and adds depth to the dish.
4. Add Liquids and Lentils (Optional): Pour in the vegetable broth and vegetarian Worcestershire sauce. If using red lentils, add them now. Bring the mixture to a simmer, then reduce the heat to low, cover, and let it simmer for 15-20 minutes, or until the lentils are tender (if using) and the sauce has slightly thickened. Simmering allows the flavors to meld together and the sauce to develop a richer consistency.
5. Add Frozen Vegetables and Thicken Sauce (If Needed): Stir in the frozen peas and frozen corn. Cook for another 5 minutes, or until the vegetables are heated through. Taste and season with salt and black pepper to your liking. If you prefer a thicker sauce, in a small bowl, whisk together the flour or cornstarch with 2 tablespoons of cold water to create a slurry. Gradually whisk the slurry into the simmering vegetable mixture and cook for 1-2 minutes, or until the sauce has thickened to your desired consistency.

Making the Mashed Potato Topping (Approx. 15 minutes):

1. Drain and Mash Potatoes: Once the potatoes are fork-tender, drain them well in a colander. Return the drained potatoes to the pot.
2. Mash Potatoes with Milk/Cream and Butter/Oil: Add the milk or cream and butter or olive oil to the pot with the potatoes. Mash the potatoes using a potato masher or a hand mixer until smooth and creamy. Season with salt and pepper to taste. For extra creamy mashed potatoes, you can pass them through a ricer. If using cheese, stir in the grated cheese into the mashed potatoes until melted and well combined.

Assembling and Baking the Shepherd’s Pie (Approx. 25-30 minutes):

1. Assemble the Pie: Pour the vegetable filling into the prepared baking dish, spreading it evenly. Spoon the mashed potato topping over the vegetable filling, starting from the edges and working your way to the center. Gently spread the mashed potatoes to create an even layer, covering the entire vegetable filling. You can create swirls or patterns on the top of the mashed potatoes with a fork for a more visually appealing presentation.
2. Bake: Bake in the preheated oven for 20-25 minutes, or until the topping is golden brown and the filling is bubbly around the edges. The baking time may vary slightly depending on your oven. Keep an eye on it and adjust the time as needed.
3. Broil for Extra Browning (Optional): For an extra golden brown and slightly crispy topping, you can broil the Shepherd’s Pie for the last 1-2 minutes of baking. Watch it closely to prevent burning.
4. Rest and Serve: Remove the Vegetarian Shepherd’s Pie from the oven and let it rest for 5-10 minutes before serving. This allows the filling to settle slightly and makes it easier to serve. Garnish with fresh chopped parsley, if desired, before serving.