Wash and cook asparagus ends (some tops can also be added) in chicken stock or heavily salted water for 25 minutes. Drain.
Mix cooked asparagus in an high powered blender.
Pass through a chinois or fine strainer.
Soup
Blend the strained asparagus juice with the cheese and fat. Season with salt and pepper to taste.
Garnishing
Make a few paper thin raw asparagus shavings using the mandoline. Keep them in cold water. Meanwhile, chop cooked asparagus.
Give a quick sautée to the chopped asparagus with some fat. Season with salt and pepper; keep warm.
Plating
Spoon out some sautéed asparagus and feta cubes in each warm serving bowl.
Right before serving, give the hot soup an emulsion, and pour in serving bowls. Top the soup with asparagus shavings, lemon zest and some crushed pistachios.
Storage
Asparagus soup can be stored for up to 3 days in the refrigerator. It can also be frozen. In this case, and upon the soup is thawed a day prior to serve, reheat it and blend.