Prepare: Mix all ingredients up to and including flour, add feta, swell with lid closed for about half an hour.
Shaping and cooking: Form gnocchi with 2 tablespoons, shape directly into the salted water. Pull gnocchi in batches until they rise to the surface. Remove with a skimmer, drain and keep warm.
Sauce: Sauté onions in warm butter or light butter. Add the potatoes and steam briefly. Extinguish with soup, simmer for about 10 minutes, stirring occasionally. Stir in watercress and spinach leaves, leave open for 2-3 min. Blend everything in hand blender, pour back into skillet, season, just until hot.
Serve: Spread sauce evenly on heated plates, add gnocchi on top, garnish, bring to table on the spot.
Tip: Did you know that one bowl of spinach already covers the entire daily requirement of vitamin K and beta-carotene?