Peel and trim the asparagus. Cut the stalks diagonally into 1/4 inch thick pieces; keep the stems and peelings. In a saucepan, combine the asparagus trimmings, onion, wine, and 6 cups of water. Bring to a boil, then cover and simmer over moderately low heat until the asparagus trimmings are tender, about 60 minutes. Pour the mixture into a blender and puree until as smooth as possible. Strain the broth through a fine sieve, pressing on the solids. Clean the pan.

Preheat the oven to 450°. Melt the butter in the saucepan over moderate heat. Whisk in the flour and cook until golden brown and nutty-smelling, about 3 minutes. Whisk in the asparagus broth until smooth and bring to a gentle simmer.

In a medium bowl, whisk the egg yolks with the lemon juice. Gradually mix in 1/4 cup of the hot broth, then whisk in half of the remaining broth. Return this mixture to the saucepan and simmer, whisking often, until hot. Season with salt.

On a rimmed baking sheet, mix the sliced asparagus with 2 tablespoons of oil and season with salt and pepper. Roast for about 8 minutes, stirring, until the asparagus is golden but still slightly firm.

In a nonstick skillet, heat the remaining 3 tablespoons of oil. Add the mushrooms and cook over moderately high heat until golden and crisp, about 8 minutes.

Transfer the roasted asparagus to shallow bowls. Pour the soup over the asparagus and top with the mushrooms. Garnish with dill and oregano before serving.