Wash thyme, shake dry, pluck leaves from the stems and chop. Mix mustard, 4 tablespoons breadcrumbs and thyme. Season with salt and pepper. Dab meat dry. Remove fat and tendons.
Season the meat all around with salt and pepper. Heat the oil in a roasting pan and fry the meat well all around. Spread mustard paste on the top of the roast beef. In a preheated oven (electric cooker: 80 °C/ convection oven: not suitable/ gas: see
manufacturer) 2 1/2-3 hours of frying. The core temperature should be about 60 °C.
Clean, wash, quarter and seed the tomatoes. Cut the flesh into strips. Cook the beans in boiling salted water for about 7 minutes. Drain and rinse in cold water. Peel shallots and garlic.
Cut the shallots into fine rings. Finely chop garlic.
Melt the butter in a large pot. Add garlic and onions and sauté. Add 5 tablespoons breadcrumbs and fry briefly. Add beans and tomatoes to the pot. Season to taste with salt, pepper, olive oil and vinegar.
Set aside covered. Lift the roast beef out of the roaster, cover with aluminium foil and let it rest for about 10 minutes.
Dissolve the roast with red wine and stock. Stir starch with a little water until smooth. Thicken the sauce with it. Bring to the boil and simmer for about 5 minutes. Season to taste with salt and pepper. Cut the roast beef and serve with beans and sauce.