Thinly slice a baguette; arrange in a single layer on a baking sheet. Brush with olive oil and sprinkle with salt. Bake at 425 degrees F until lightly golden, about 7 minutes. Let cool slightly.
Toss halved asparagus spears with olive oil, salt and pepper on a baking sheet. Roast at 450 degrees F until slightly crisp, 7 minutes. Spread softened butter on the toast rounds. Top with sliced prosciutto and the roasted asparagus.