Trim the fat from the beef cheeks.

Heat the oil in a rondeau or braiser until it starts to simmer. Place the beef cheeks carefully in the oil to sear to a deep brown on all sides. Remove to a pan and reserve.

Add the mirepoix to the pan and cook, stirring from time to time, until the onions are golden brown, about 7 to 8 minutes. Add the tomato puree and cook until it turns a deeper color and gives off a sweet aroma, about 1 minute.

Add the wine to the pan, stirring to release any dripping. Reduce by half. Return beef cheeks to the pan along with any juices they may have released. Add the stock to cover them by two-thirds.

Bring to a gentle simmer over medium to low heat and add the sachet. Cover the pot and transfer it to a moderate oven (300F). Braised the beef cheeks for 3 hours and add the vegetables. Continue to braise until the meat is fork tender and the vegetables are fully cooked, turning the beef cheeks occasionally to keep them evenly moistened.