Clean, wash and shake spinach dry. Wash meat, dab dry, cut into cubes. Peel and finely chop the onion.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Heat the oil in a large pan and fry the meat for approx. 4 minutes. Finally fry the onion briefly. Season with salt and pepper and dust with flour. Deglaze with milk, bring to the boil while stirring, fold in spinach in portions so that it collapses. Season to taste with nutmeg, salt and pepper. Fold in gnocchi.
Spread the gnocchi casserole in a casserole dish. Grate the gouda roughly and sprinkle over the casserole. Bake in a hot oven for about 30 minutes.