Clean and wash the celery, cut it into pieces and stew it in a pot with little water for 10-12 minutes until al dente. Meanwhile clean the cauliflower, divide into small florets and wash.
Cook in boiling salted water for about 10 minutes. Remove the celery and rinse with cold water. Heat the oil in a coated pan, fry the minced meat for 3-4 minutes, season with salt and pepper.
Remove the cauliflower and rinse with cold water. Measure out 1/4 litre of vegetable water. Melt the fat in a pot and sauté the flour in it. Deglaze with vegetable water and milk while stirring. Season with salt, pepper and nutmeg.
Cut 3/4 of the cress from the bed and fold into the sauce. Grease a large casserole dish. Put cauliflower, minced meat and celery in it and pour the sauce over it. Grate the cheese and spread it on top.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes. Remove the casserole. Cut the rest of the cress from the bed and sprinkle over the casserole.