Wash the meat, dab dry and season all around with salt and pepper. Place on the fat pan of the oven and bake in the preheated oven (electric: 200 °C/ gas: level 3) for approx. 1 1/4 hours.
Gradually add about 1/2 litre of water. Defrost the spinach. Wash the potatoes and cook in salted water for about 20 minutes. Quench cold and remove the skin. Heat oil in a pan and fry the potatoes in it at medium heat until golden brown all around.
Season with salt. Remove potatoes from the pan and keep warm. Peel onions and cut into slices. Fry in the frying fat at medium heat. Add spinach and steam for about 4 minutes. Add cream and stir in carefully.
Season to taste with salt and pepper. Remove the roast. Pour frying stock through a sieve and fill up to 1/2 litre with water. Pour into a pot, bring to the boil and thicken with sauce thickener. Season to taste with salt and pepper.
Serve the roast, spinach and potatoes arranged on a plate.