Heat the oven to 250 F.
Heat the olive oil in a large Dutch oven, such as Le Creuset. Add the bacon and cook over medium heat for 8 to 10 minutes, stirring occasionally, until the bacon is lightly browned. Remove the bacon with a slotted spoon to a large plate.
Dry the beef cubes with paper towels and then sprinkle them with salt and pepper. In batches in single layers, sear the beef in the hot oil for 3 to 5 minutes, turning to brown on all sides. Remove the seared cubes to the plate with the bacon and continue searing until all the beef is browned. Set aside.
Toss the carrots, onions, 1 teaspoon of salt and 1 teaspoon of pepper into the fat in the pan and cook over medium heat for 10 to 12 minutes, stirring occasionally, until the onions are lightly browned.
Add the garlic and cook for 1 more minute.
Add the Cognac, stand back, and ignite with a match to burn off the alcohol.
Put the meat and bacon back into the pot with any juices that have accumulated on the plate.
Add the wine plus enough beef broth to almost cover the meat.
Add the tomato paste and thyme.
Bring to a boil, cover the pot with a tight-fitting lid and place in the oven for about 1 ¼ hours, or until the meat and vegetables are very tender when pierced with a fork. Remove from the oven and place on top of the stove.
Combine 2 tablespoons of the butter and the flour with a fork and stir into the stew.
Add the frozen onions.
In a medium pan, sauté the mushrooms in the remaining 2 tablespoons of butter over medium heat for 10 minutes, or until lightly browned, and then add to the stew.
Bring the stew to a boil, then lower the heat and simmer uncovered for 15 minutes. Season to taste.
Rub each slice of bread on one side with garlic. For each serving, spoon the stew over a slice of bread and sprinkle with parsley.