In 's Gravenvoeren, I ate at lunch inHotel Brasserie Blanckthysasparagus à la flamande. They were crisp.
When the patron asked if everything was satisfactory, I also replied along those lines. And he revealed his secret, which I may post with his permission. You can also find it on the Internet, of course .
The asparagus will be served with a knob of butter in a vacuum bag stabbed which is sucked airless. They are then cooked in their own juice in a steam oven at 88°. They are either used shortly afterwards or frozen. Even from the freezer, they remain crisp when you reheat them in the vacuum bag. That way, none of their flavour is lost in cooking water.