In a large skillet or Dutch oven, heat the olive oil and add as many meat cubes as you can without crowding (if the skillet is too crowded, the meat won't brown properly.) Brown the meat well on all sides, remove each batch as it browns and set them aside. It may be necessary to add a little olive oil.
When all of the beef has been browned and removed, add the onions to the remaining juices in the skillet and cook, stirring occasionally, until they are golden brown. Add the thyme and the mushrooms and cook until they have released most of their water. Add the tomato puree, garlic and when garlic is fragrant add the white wine and let it cook for a couple minutes. Add the carrots and the reserved beef pieces (if you did them in a separate fry pan). Add the brown sugar, stock and salt and pepper to taste.
Add the flour the same way we do it on the video to thicken.
Bring to boil, reduce to low heat, and cook for about 2 ½ to 3 hours or until the beef tender enough to cut with a spoon. Be sure to check every so often to make sure the beef does not attach at the bottom.
Add the mustard, and a little sour cream. Mix well and serve with a large fettucine like pappardelle top with more sour cream and sprinkle with freshly chopped chives.
