Bring a large pot of water to a boil. Season generously with salt and add the parsnips. Boil until the parsnips are as soft as butter, 10 to 15 minutes. If certain pieces are still hard while others are tender, pull out the tender ones, and allow the tougher ones to cook another 5 minutes. It's really important to cook the parsnips until they're lusciously soft, or else your hummus will be stodgy.
Drain the parsnips, saving about 1 cup of the hot water. Toss the parsnips into a food processor along with the tahini, olive oil, garlic, lemon juice and 1/4 cup of hot water. Puree until smooth. Taste for seasoning, and depending on how salty your tahini is, adjust the salt and pepper accordingly.
Serve warm or at room temperature. I like to pile the hummus into a shallow bowl, forming a small pool in the middle. Pour a little olive oil into the pool and sprinkle with a little paprika. Serve alongside a gorgeous platter of vegetables.
Tahini is paste made of hulled, lightly toasted sesame seeds. Make sure you read the ingredients on the jar you're buying. It should only list the seeds and nothing else!