In a large frying pan, heat oil over medium-high heat. Add shanks to hot pan, and brown all sides; this should take about 12 minutes. Transfer to a plate.
Reduce heat to medium-low, and add garlic to the pan; cook for 30 to 40 seconds. Stir in onion, and continue cooking until translucent, 6 to 8 minutes. Return shanks to the pan, and season with 2 teaspoons fresh rosemary and salt and pepper to taste. Pour in wine, raise heat to medium-high, and bring to a simmer. Reduce heat to low, cover tightly, and simmer until the shanks are very tender when pierced with a knife, 2 to 2 1/2 hours. Turn once or twice during cooking, and add water as necessary to maintain original level of liquid. Serve shanks garnished with rosemary sprigs.