Vegetables:

Grease a 9- x 13-inch pan with evoo.

Heat a large sauté pan, lightly coated with evoo, over medium-high heat. Sauté onions, leeks, carrots, mushrooms, and squash in batches until golden brown. Be sure to season each batch with salt and pepper.

Add garlic toward the end of last batch of vegetables so that it doesn't burn. Sauté garlic with vegetables for just 2 to 3 minutes until it begins to soften. Add wine to deglaze the pan and allow wine to evaporate by half.

Toss sautéed vegetables with parsley, thyme, lemon zest and tomato paste. Transfer vegetables to greased pan.

Creamy Mashed Potatoes and Chestnuts:

Preheat oven to 350°F. 

Heat a Dutch oven, lightly coated with evoo, over medium heat. Sweat shallots and garlic until translucent, about 5 minutes. Add potatoes, chestnuts, and just enough water to barely cover potatoes.

Cover, reduce heat to low, and simmer until potatoes are very creamy and most of the liquid has been absorbed.

Using a potato masher, mash potatoes and chestnuts until a creamy puree is formed, adding additional evoo if necessary. If potatoes are very wet, reduce heat to low and cook, uncovered, stirring frequently to evaporate water. Season with salt and pepper. 

Pile potato puree on top of vegetables and smooth down the surface. Drizzle with evoo and bake at 350°F for 30 to 40 minutes or until lightly browned and vegetables are bubbly.