Melt 3 tablespoons butter with oil in large pot over medium heat. Add onion; saute until soft, about 5 minutes. Add parsnips, potatoes, and turnips; stir 4 minutes. Add garlic; stir 1 minute. Add broth; bring to boil. Cover; reduce heat to medium-low. Simmer until vegetables are tender, about 15 minutes. Using slotted spoon, transfer vegetables to large bowl. Pour cooking broth into small bowl; reserve. Add cream cheese to vegetables. Using electric mixer, beat vegetables to smooth puree. Add 2 tablespoons butter-oil mixture from top of broth to vegetables. Stir in 2 tablespoons dill. Season with salt and pepper. Butter 11 x 7 x 2-inch glass baking dish. Transfer puree to prepared dish. DO AHEAD: Can be made 1 day ahead. Cover and chill. Melt 3 tablespoons butter in small skillet over medium heat. Add panko and stir until golden brown, about 2 minutes. DO AHEAD: Can be made 1 day ahead. Cool and store airtight at room temperature. Position rack in top third of oven; preheat to 350°F. Sprinkle panko mixture over vegetable puree. Bake until top is brown, about 15 minutes (25 minutes if chilled). Sprinkle with 2 tablespoons dill.