2 Tbs. unsalted butter
1/2 cup chopped onions
2 cloves garlic
1 Tbs. minced fresh ginger root
3 cups chopped peeled parsnips, about 2 lbs. whole parsnips
1 cup freshly squeezed white grapefruit juice, about 2 lbs. whole grapefruits
3 cups low-sodium chicken stock
3/4 cup crème fraîche (or sour cream), divided
2 tsp. kosher salt
1 tsp. grapefruit zest, plus more for garnish
Cracked black pepper
4 grapefruit segments for garnish
Heat the butter in a medium saucepan over low heat. Add the onions, garlic, ginger, and parsnips and, stirring occasionally, cook over low heat until the onions are translucent, about 10 minutes. Add the grapefruit juice, increase the heat to high, and let briskly simmer until the liquid is reduced to a half a cup. Add the chicken stock, lower the heat to medium, and simmer the soup for 10 minutes.
Working in batches with solids and liquids in each, carefully transfer the hot soup to a blender and puree it until smooth. Add half a cup of the crème fraîche and pulse until combined. Return the soup to the saucepan. Add the salt and grapefruit zest and stir well to combine, making sure that the crème fraîche is well blended. Taste for seasoning and add more if desired.
Serve in warm bowls and garnish with a tablespoon of crème fraîche, a sprinkling of black pepper, a grapefruit segment, and a few zest slivers.