How to Make It
Preheat the oven to 350°. In a large skillet, heat the 3/4 cup of olive oil with the garlic and cook over moderate heat until the garlic is golden. Using a slotted spoon, remove the garlic and reserve for another use. Add half of the parsnips to the skillet and cook over moderate heat, stirring occasionally, until golden and barely tender, about 12 minutes. Using a slotted spoon, transfer the parsnips to a roasting pan. Repeat with the remaining parsnips, then scrape the parsnips and any oil into the roasting pan. Add the dates and marjoram sprigs, season with salt and pepper and roast for about 8 minutes, just until the parsnips are tender and the dates are slightly caramelized. Transfer the parsnips and dates to a platter.
In a bowl, whisk the yogurt with the lemon juice, sumac and the remaining 2 tablespoons of olive oil. Season with salt. Serve the roasted parsnips and dates, passing the spiced yogurt at the table.
The cooked parsnips and spiced yogurt can be refrigerated separately overnight. Rewarm the parsnips before serving.
Ground sumac is made from a tangy dried berry. It is available at specialty shops and Middle Eastern markets and online at chefshop.com.