Rinse fresh spinach. Place dripping wet in a frying pan and steam until just tender and collapsed. Drain, squeeze very well and chop into small pieces.
Defrost frozen spinach and squeeze very well in a kitchen towel as well.
Put the flour in a suitable bowl. Mix water, milk, eggs and salt, add and beat everything together for two to three minutes until it forms a thick dough. At the end, stir in the spinach.
Preheat the oven to 100 °C. Heat a buttered casserole dish.
Bring plenty of salted water to the boil. Put the dough in batches on a kitchen board, brush it into the boiling water or rub it through the spaetzli sieve and do this only until the knöpfli rise to the surface. Lift out with a skimmer and drain well. Place in layers in the preheated dish and grate enough Schabziger over each unit. Keep the Knöpfli warm.
Remove the skin from the onion and cut into narrow rings. Roast in the butter until light brown and spread evenly over the Knöpfli. Serve immediately.
Tip: Did you know that one bowl of spinach already covers the entire daily requirement of vitamin K and beta-carotene?