My mother-in-law always cooks great meals for us when we come to visit. She recently cooked a wonderful sweet potato soup that I thought would be great in a modernist preparation. I've roasted the sweet potatoes and added some molasses, ginger, and thyme for extra depth of flavor.
Once the soup is done you add it to your whipping siphon and foam it into the bowl. The foaming processes helps lighten the soup and give it a more airy texture than is expected.
This sweet potato soup foam is also great as a hearty sauce on meats or vegetables. You can even use it as a dip at parties.
If you like this recipe you can get it and more than 50 other recipes from my book Modernist Cooking Made Easy: The Whipping Siphon. The book covers the three main uses of the whipping siphon: foaming, carbonating, and infusing. It is all presented in an easy to understand format that anyone can follow.
Also, if you are just getting started experimenting with molecular gastronomy and modernist cuisine then I highly recommend one of these molecular gastronomy kits. They have everything you need to do many different dishes.
Preheat an oven to 232°C / 450°F.
Toss the sweet potato chunks with canola oil and salt and pepper. Spread out on a sheet pan and roast until the outsides have browned nicely, typically 20 to 30 minutes.
Place the roasted sweet potatoes into a pot with the chicken stock, ginger, molasses, and thyme. Cook until the sweet potatoes are very soft and the flavors have melded. Start with 200 grams of stock and add more as needed to keep it moist. Add the honey and cream then puree until very smooth using a blender. Strain through a chinois or cheese cloth if you want a finer texture.
Pour the sweet potato soup into your whipping siphon and charge. If desired, heat the whipper in hot water until it is warm.
Dispense the soup into soup bowls or cups. Top the soup with the marshmallows, thyme leaves, and walnuts then finish with a drizzle of molasses.