Preheat the oven to 400 degrees F.
Arrange the asparagus on a rimmed baking sheet, in a single layer, and drizzle with 1 tablespoon of olive oil. Season with salt and pepper, to taste, and roll the stalks around to coat evenly. Transfer the pan to the oven and roast, shaking the pan several times to turn the asparagus, until the tips are browned and crisp, 15 to 20 minutes.
Meanwhile, heat the remaining 1 tablespoon of oil in a saucepan over medium heat. Add the shallots and cook until softened, 3 to 4 minutes. Add the rhubarb and cook an additional 2 to 3 minutes. Stir in the vinegar and simmer until the rhubarb is broken down but not mushy and the flavors are infused, 10 to 12 minutes. Strain the mixture through a fine mesh strainer into a small saucepan. Bring the mixture to a simmer over medium-low heat and simmer until thick and syrupy, about 5 minutes.
To serve, arrange the asparagus on a large platter, drizzle with the rhubarb vinegar and season with salt and pepper, to taste.
Recipe courtesy of Claire Robinson, 2009