Friday, March 14, 2014

Hot Potatoes (Sweet Potato Chipotle Soup)

Lately, I've been obsessing over soups. The perfect answer to blinding snow and biting cold, they make a timely and seasonally appropriate companion. The winter pantry offers no short stock of roots like onions, potatoes, and garlic, and hardy greens like cabbage and kale, but today I extoll the virtues of the humble sweet potato. Naturally bursting with flavor and nutrients, sweet potatoes make a thick, velvety soup with a color sure to brighten up the end of the day. Some of the oldest evidence of human sweet potato consumption dates from Peru 8,000 years ago, spreading to the Caribbean by 2500 BC and Polynesia by 1000 AD. Europeans weren't lucky enough to first taste sweet potatoes until Columbus' famed voyage of 1492. I embraced a general Meso-American theme by including Mayan sweet onion and the smoky spice of chipotles in adobo.

Colorful, flavorful
Today, sweet potatoes are grown throughout all the tropical and warm temperate regions of the world, from Japan to Burundi. China is the world's top producer, accounting for nearly 83% of the world's sweet potatoes, while North Carolina is the sweet potato capital of the US, accounting for nearly 40% of domestic harvests. Their popularity in the American south, where they are also known as yams, has led to a confusion of nomenclature. True yams, which sweet potatoes are not even remotely related to but were considered to superficially resemble, are native to Africa and Asia, tend to grow much longer (up to five feet!), have a drier, more starchy texture, and lack the characteristic sweetness. To try and clear up matters, the USDA requires all sweet potatoes labeled as "yams" must also carry the label "sweet potatoes."

Hot potatoes
In addition to its geographic domination, the sweet potato lends itself to a miraculous variety of culinary interpretations, from the savory to the sweet. Simple roasted sweet potatoes are a popular winter street food in China and Egypt (a trend I certainly wish would catch on in the US), but they are also processed into noodles, pastries, jellies, soups, cakes, chips, breads, pies, and casseroles. The characteristic sweetness that makes sweet potatoes so versatile comes from their unique chemical makeup. Like most tuberous vegetables, sweet potatoes store energy in their roots as starch. In their particular case, the starch in question is called amylose. Coincidentally, sweet potatoes are also naturally rich in amylase, the enzyme that breaks down amylose. The result is less bland amylose starch and more sticky-sweet maltose sugar for us to enjoy.

Onions also carry substantial sugars, just cook off the sulfur for savory sweetness
Heat speeds up the breakdown of starch into sugar, and the slower the cooking process, the longer the amylase has to do its thing, resulting in a sweeter potato. This is why baking and roasting often prove the sovereign method of preparation. The good news is baking is a hands-off process, so once the potatoes pop out of the oven, already gooey-soft, an immersion blender makes short work of them. This is a very quick and easy soup that can be thrown together in an hour. Sweet onions and soft potato make for a rich, creamy texture without needing to add the fat and cholesterol of dairy, so this is one dinner you can enjoy guilt-free. Perfectly paired with a green salad or quesadilla (in a southwestern update of the classic couple of grilled cheese and tomato soup), this soup is just the thing to spice up an evening.

Ready for nom
Sweet potato chipotle soup

You can hoard pre-cooked sweet potatoes as an easy make-ahead trick, but the soup itself can also be made ahead and kept refrigerated for several days. Serves 4-6.

3 large sweet potatoes
Extra virgin olive oil, to coat

4 cups vegetable stock
1 tablespoon extra virgin olive oil
1 large sweet onion, sliced
3 cloves garlic, chopped
3-4 chipotles in adobo
1 teaspoon ground cumin
Sea salt and freshly cracked black pepper, to taste

Preheat an oven to 375 F, rub the potatoes with a small amount of extra virgin olive oil, prick them several times with a fork, and wrap tightly in aluminum foil. Roast potatoes in the oven for about 45 minutes, until completely softened and sliding out of their skins.

Rich, peppery goodness
Set the potatoes aside to cool slightly and warm the vegetable stock in a small pot on medium while you heat the oil in a larger pot. When the oil is shimmering, toss in the onions and cook, stirring occasionally, until translucent, about five minutes.

Add the garlic and chipotles, then cook a few minutes more. Scoop the sweet potato flesh out of their skins and into the pot, mashing with a spoon.

Uncensored carnage
Carefully pour in the hot stock and add the cumin. Use an immersion blender to puree the entire soup until smooth and creamy. Season to taste with salt and pepper.

Serve hot, garnished with fresh avocado and/or tortilla strips.

 Also available from the Williamsport Sun-Gazette.

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