Peel and trim the asparagus. Slice the stalks diagonally 1/4 inch thick; reserve the stems and peelings.

In a saucepan, combine the asparagus trimmings, onion, wine, and 6 cups of water. Bring to a boil, then simmer, covered, over moderately low heat until the asparagus trimmings are soft, about 1 hour.

Transfer the contents to a blender and puree until smooth. Strain through a fine sieve, pressing on the solids. Wipe out the pan.

Preheat the oven to 450°F. Melt butter in the saucepan over moderate heat. Whisk in 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 bowl, whisk the egg yolks with lemon juice. Gradually whisk in 1/4 cup hot broth, then half of the remaining broth. Return this to the pan and simmer, whisking, until hot. Season with salt.

On a rimmed baking sheet, toss sliced asparagus with 2 tablespoons olive oil, salt, and pepper. Roast for about 8 minutes, stirring occasionally.

In a nonstick skillet, heat remaining 3 tablespoons olive oil. Cook mushrooms over moderately high heat until golden and crisp, about 8 minutes.

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