Wash the meat and dab dry. Rub with salt and pepper. Mix mustard, oil and parsley. Spread the meat with it and cover with slices of bacon. Place on the fat pan of the oven and bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) approx.
Pour in the stock little by little. In the meantime peel onions, clean and peel carrots. Cut both into small pieces and distribute around the meat after about 20 minutes frying time. Clean and wash the Brussels sprouts and cook them in about 1/2 litre of boiling salted water for about 20 minutes.
Wash the thyme, dab dry and remove the leaves from the stems. Sprinkle leaves on the roast about 10 minutes before the end of the frying time. Drain the brussels sprouts and collect the vegetable water.
Remove the roast and keep it warm. Fill up the roast stock with onions and carrots to 1/2 litre with the vegetable water and puree everything with a chopping stick. Bring to the boil and sprinkle in sauce thickener while stirring.
Bring to the boil again and season to taste with salt and pepper. Heat the fat. Brown breadcrumbs in it, add Brussels sprouts and toss in. Cut the roast open and arrange on a plate with the sprouts and some sauce.
Possibly serve garnished with parsley. Serve the rest of the sauce separately. Roasted potato wedges taste good with it.