Global markets and high-tech shipping methods have put asparagus on our tables virtually year-round, yet most of us still associate it with spring.

But whenever you eat it, asparagus is a nutritional powerhouse. It is low in calories (about 5 calories per stalk) and is packed with vitamins A, C and E, and folate.Green, purple and white varieties of asparagus are common, though green is the least expensive and most readily available. Green asparagus has a fresh, woodsy flavor, while purple varieties tend to have a more fruity flavor. White asparagus is milder in flavor and should always be peeled before cooking.When shopping for asparagus, look for firm stalks with tight tips. Fresh asparagus should snap when bent. Though best eaten the day purchased, asparagus can be refrigerated, wrapped in a damp cloth inside a plastic bag, for three days.Though not essential, peeling tough-skinned stalks with a vegetable peeler will help ensure that the tips and otherwise thicker stalks cook at the same rate. And be sure to rinse all asparagus thoroughly before cooking to remove any lingering sand.For this simple asparagus and potato soup, all the vegetables are roasted at high heat, caramelizing their natural sugars and enhancing the flavors. They then are pureed until smooth and combined with thick, nonfat Greek-style yogurt, which gives the soup a creamy quality that belies its low-fat nutritional profile.To top off the soup, shreds of sweet and salty prosciutto ham are crisped in a skillet to create a garnish that has all the appeal of crumbled bacon, without all the grease.Roasted asparagusand potato soupStart to finish: 1 hour (15 minutes active)Servings: 46 cloves garlic1 pounds asparagus, bottoms trimmed, cut into 1-inch pieces (about 3 cups)2 cups peeled and diced Yukon Gold potatoes1 medium sweet onion, cut into 6 wedges1 tablespoon extra-virgin olive oil1/2 teaspoon salt, plus more to taste1/2 teaspoon ground black pepper, plus more to taste2 ounces prosciutto, chopped3 cups chicken broth, divided6 ounces nonfat plain Greek-style yogurt1 teaspoon lemon juice1 tablespoon minced fresh tarragonHeat the oven to 425 F.Place the garlic on a square of foil and sprinkle with 1 teaspoon water. Fold the foil into a packet. Set aside.In a large bowl, combine the asparagus, potatoes, onion, oil, 1/2 teaspoon salt and 1/2 teaspoon of black pepper. Toss to coat. Spread the vegetables over 2 large, rimmed baking sheets. Place the packet of garlic in one corner of one of the sheets. Roast, stirring occasionally, until the asparagus pieces are soft and the potatoes are tender, 35 to 45 minutes.Meanwhile, in a small skillet over medium, crisp the prosciutto, about 5 minutes per side.When the vegetables are roasted, empty the garlic onto the baking sheet with the other vegetables and cool for 5 minutes.Transfer half of the vegetables into a blender. Add 1 1/2 cups of the broth, then blend until smooth. Transfer to a large pot. Repeat using the remaining vegetables and remaining 1 1/2 cups of broth. Warm the soup over medium heat.Whisk the yogurt, lemon juice and tarragon into the soup. Season with salt and pepper to taste. Crumble the prosciutto and use to top each serving.Nutrition information per serving (values are rounded to the nearest whole number): 233 calories; 53 calories from fat (23 percent of total calories); 6 g fat (1 g saturated; 0 g trans fats); 12 mg cholesterol; 33 g carbohydrate; 13 g protein; 5 g fiber; 1,355 mg sodium.