All through the summer, I make a weekly trip on my bike to the Union Square Greenmarket. I always stop at Keith Stewart's stand to buy his amazing garlic, tomatoes, lettuces, and herbs. Just about every week, there are new offerings, so that I can gauge the progression of the season well into fall, when cool-weather vegetables like celery root and potatoes determine my cooking. Lately, I've been making Root Vegetable Crema, a velvety pureed soup that can be made with an endlessly variable mix of root vegetables such as potatoes, parsnips, celery root, and leeks. It makes a fine simple supper or satisfying first course for a dinner party.
This simple root vegetables soup achieves its extraordinary creaminess from a technique I developed in A New Way to Cook to concentrate the flavor of vegetables: braise the root vegetables slowly in water with a little butter. The small amount of fat suffuses the vegetables and gives them a rich, dense texture, delicious as is or enriched with a dollop of crème fraiche or whipped cream. The idea for this soup came from Paul Bertolli when he was chef at Chez Panisse in Berkeley, California. He used the suave puree as a medium for a fresh black truffle that he had pounded to a paste in a mortar to make an astonishing soup: truffle and root vegetable enhancing each other. The barest drizzle o white truffle oil is also divine.