Begin by peeling and quartering the Yukon gold potatoes. Place them in a large pot with enough cold water to cover, adding 1 teaspoon of salt. Bring to a boil and cook until fork-tender. While the potatoes cook, dice the carrots and finely chop the mushrooms. Thinly slice the shallots and measure out the remaining liquid ingredients, so everything is ready to go.

Once the potatoes are tender, drain them thoroughly and return them to the hot pot. Mash them well, then stir in the butter and room-temperature Greek yogurt until smooth and creamy. Season with salt to taste. While the potatoes are still warm, I really like to get them seasoned properly now to ensure maximum flavor in every bite. Set the mashed potatoes aside.

In a large, heavy-bottomed pot or Dutch oven, heat the olive oil over medium heat. Add the sliced shallots and cook until fragrant and softened, about 3-4 minutes. Next, add the chopped mushrooms, diced carrots, rosemary, thyme, and bay leaf. Cook, stirring occasionally, until the carrots begin to soften, creating a deeper flavor in the base. I always sauté my vegetables until they are nicely browned as this caramelization brings so much more depth to the dish.

Stir in the tomato paste and flour into the cooked vegetables, cooking for 1 minute to toast the flour lightly. Pour in the red wine, scraping up any browned bits from the bottom of the pot, and let it cook down for 1-2 minutes. Gradually add the vegetable broth, stirring constantly until the gravy thickens to your desired consistency. Season the gravy with salt.

Once the gravy has thickened, remove the rosemary sprig, thyme sprig, and bay leaf. Stir in the thawed frozen peas. Transfer this savory vegetable filling to an oven-safe baking dish. Evenly spread the prepared mashed potatoes over the top of the filling, making little peaks with a fork for texture. Bake in a preheated oven at 350°F (175°C) for about 15 minutes, until heated through. For a golden crust, I recommend finishing it under the broiler for a few minutes, watching carefully to prevent burning.