Preheat oven to 375 F. Cut the very top off the garlic bulb to expose the tops of the cloves. Place in a ramekin and drizzle with olive oil and sprinkle with sea salt. Cover ramekin with tin foil.
Place Garlic in oven to roast for about 45 to 60 minutes or until cloves are soft and squeezable. Place turnips in a steamer over hot water and steam for about 20 minutes or until soft but not mushy.
Mash the turnips with a potato masher until smooth. Add butter, chopped lemon thyme, garlic that you've squeezed out of the bulb, sea salt and pepper and mix well.