Boil the potatoes. Add the potatoes to a large pot and over them with water. Place the pot on the stovetop and bring it to a boil, then cover the potatoes and let them cook on low heat for about 15 minutes, until they are fork tender. Drain the potatoes and add them back to the pot.

Use a potato masher or fork to mash the potatoes. Make sure to mash them while they are nice and hot.

Stir in the butter, olive oil, milk, salt and pepper. Set aside.

Heat the oil and butter in a large pan on the stovetop then add the shallots and cook until they are soft and translucent. Add in the sliced mushrooms and carrots and toss and cook until the mushrooms and carrots are soft and starting to brown. Add the garlic and thyme and cook for one minute. Season the veggies with some salt and pepper.

Stir in the flour and tomato paste and whisk in the vegetable broth while scraping the brown bits of flavor off of the bottom of the pan. Continue to stir while the sauce thickens and season it with more salt and pepper. Then stir in the peas and corn and let it cook for 2 minutes.

Pour the filling into a sprayed oven safe dish and spread it out evenly in the pan. Layer on the mashed potatoes and spread them out so they cover all of the filling.

You can either spray the top with olive oil spray or melted butter and sprinkle it with a little paprika. Then place the casserole into a 350 degree oven and bake it for 15-20 minutes. If you prefer the top to be extra golden then place it under the broiler for the last 5 minutes of cooking time. Remove, let cool and serve.