Preheat oven to 400°F (200°C). Toss the parsnip and potato peels, garlic, shallot, olive oil, 1/2 tsp each of the salt and pepper and the 2 tsp of thyme, on a parchment-lined baking sheet. Bake for 10 min, stir and bake for another 8 to 10 min or until golden brown and crispy. Set aside.
Add the parsnip, potato and rutabaga chunks, rosemary and thyme sprigs to a large saucepan with the broth and add 2 cups of water. Bring to a boil over high heat, reduce and simmer for about 20 min or until vegetables are very tender. Drain, reserving cooking liquid.
Return vegetables to saucepan with 1/2 cup reserved cooking liquid, the sour cream, melted butter and remaining salt and pepper. Mash or beat with a mixer until vegetables reach the desired consistency.
Transfer to serving dish and top with half the crispy vegetable topping. Serve the remaining crispy vegetable topping on the side.
The mash and topping can be made up to two days in advance. To serve: Place the mashed root vegetables in an ovenproof serving dish and reheat in a preheated 350°F (180°C) oven for 15 to 20 min until mixture is warmed through. Spread the topping on a baking sheet and reheat for 3 to 5 min or until topping is crispy.