Steam the asparagus until tender. Refresh briefly in icy cold water and drain well. Trim each asparagus spear to about 11cm in length. (Reserve trimmings eg. for salads or omelettes.)
Make the salsa Verde by processing the parsley, mint, anchovies, lemon zest and juice until blended but not totally smooth. Add the olive oil in 2 lots. Quickly pulse in the capers and mustard. Transfer salsa to a bowl and season with salt and pepper to taste.
Butter the bread then cut each slice in half.
Toss asparagus with salsa Verde to coat well. Roll each spear in a piece of bread to make a neat roll. Store under a barely-damp cloth until serving.
Serves 10 – 15.
[OR Toss spears in salsa Verde and arrange in a pile on a platter - serves 8 as part of an antipasto selection. Allow 3 spears of asparagus per person for a party.]