Preheat oven (electric cooker: 80°C/circulating air and gas not suitable). Dab meat dry and rub with salt and pepper. Heat lard in a roaster. Brown the meat in the roaster for about 10 minutes.
Cook in a hot oven for 2 1/2-3 hours.
In the meantime, wash the herbs for the sour cream and shake dry. Finely chop the chives and dill. Chop parsley finely. Peel and chop onion. Mix quark and crème fraîche. Stir in onion and herbs.
Season to taste with salt and pepper.
Peel the garlic and cut into thin slices. Peel and wash the potatoes and cut them into halves or quarters depending on their size. Cover with garlic and cook in boiling salted water for about 20 minutes.
Wash the pumpkin, quarter lengthwise and remove the seeds with a spoon. Wash the rosemary, dab dry and remove the needles. Drain the potatoes. Add 2 tablespoons of butter and let it melt. Cover the potatoes and shake them vigorously in the pot and place them on a baking tray with the pumpkin.
Spread 2 tablespoons of butter in flakes on top.
Remove the roast beef from the oven. Turn up the oven (electric cooker: 225°C/circulating air: 200°C/gas: level 4). Bake in the oven with potatoes and pumpkin for 30-35 minutes. Wrap roast beef in aluminium foil and dish towels, let rest for about 35 minutes.
After 15 minutes, turn the pumpkin and potatoes and spread rosemary on top. Cut the roast beef. Arrange everything. Sprinkle with sea salt. Add the sour cream.