Place the beef in a large bowl and add all the marinade ingredients. Cover and marinade for at least 8 hours or preferably overnight, refrigerated.
Drain off the liquid from the marinade and reserve. Remove the peppercorns, onions, and garlic. Separate vegetables from the meat. Dry the meat thoroughly on paper towels.
Heat a heavy bottomed saucepan. Add the butter and oil, then add in the beef. Cook over a high heat until seared all over, then remove from the pan and keep warm. Add the lardons and cook for 3 to 4 minutes, until golden. Add the shallots and cook until they just begin to soften. Stir in all the marinade vegetables, and cook for a further 3 to 4 minutes. Return the meat to the pan and season generously with salt and pepper and stir in the mustard until all the ingredients are coated generously. Pour in the reserved marinade liquid and bring to a gentle bubble. Cover with a lid and cook for 1 1/2 to 2 hours, the sauce should be thick and the meat tender. You may need to add a little water half way through the cooking process. Serve with mashed potatoes.
Cook the potatoes in salted boiling water for 12 to 15 minutes until tender.
Heat the cream and butter together until the butter is thoroughly melted. Blanch the herbs in boiling salted water 2 to 3 minutes. Drain and rinse thoroughly under very cold water until completely cooled. Place blanched herbs in a blender and puree. Slowly add the olive oil, while the motor is still running, to form a smooth puree.
Mash the potatoes, then add butter and cream. Stir thoroughly until you have a smooth paste. Finally fold in herb puree and season generously. Mix well to form a green smooth mash.