- Preheat oven to 300 degrees. Light grill or preheat grill to medium. Peel parsnips, and then quarter lengthwise. Drizzle with grapeseed oil, salt, and pepper.
- Place parsnips on grill over medium heat and cook until almost tender. Transfer to an 8×8-inch baking pan. Add vegetable stock and garlic and cover. Bake until very tender, 30 minutes.
- Remove parsnips from pan and purée in blender until smooth, using remaining cooking liquid as needed to achieve a smooth consistency. Season to taste.
- Season shrimp with salt and pepper and toss with grapeseed oil. Grill over medium heat until cooked through.
- Sauté black trumpet mushrooms over medium-high heat. Season with salt and pepper.
- To serve, top purée with shrimp, mushrooms, and clementine segments.