Soup greens and onions clean or peel, wash and chop. Distribute in a large roaster (with lid).
Wash the meat, dab dry and tie into shape with kitchen string. Mix mustard, 4 tsp paprika, 2 tsp salt, 1-2 tsp pepper and 100 ml beer. Coat the roast all around with it. Put it on the vegetables and pour the rest of the beer.
Covered in a hot oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) and roast for approx. 1 3⁄4 hours. Then dissolve stock in 1⁄2 l hot water and pour onto the meat. Increase temperature to 200 °C (fan oven: 175 °C/gas: level 3) and roast open for another 30-40 minutes.
Remove meat and keep warm. Sieve the roast stock, bring to the boil. Mix starch with 4-5 tablespoons of water and thicken the stock. Season sauce with salt, pepper and 1 pinch of sugar. Arrange everything.