Bring an inch of water to a boil in a saucepan just large enough to hold the turnip chunks in a single layer. Add a generous pinch of salt, add the turnips, then layer the cauliflower on top. Sprinkle with salt, cover, and cook until very tender and just slightly overcooked. Drain in a colander. When cool enough to handle, add the veggies to a food processor with the remaining ingredients. Depending on the size of your food processor, you may have to partially process half of them before you can add the rest. Process until completely smooth. Taste and add salt if desired. Serve warm, optionally sprinkled with truffle salt.