Preheat the oven to 250 degrees.
Heat the oil in a large stock pot or Dutch oven over medium heat. Add the bacon and cook until lightly browned, stirring occasionally. Using a slotted spoon, remove the bacon from the pot and transfer to a large plate (leave the bacon fat on the bottom of the pan). Return the pot to medium heat.
Pat the beef cubes dry with paper towels and season with salt and pepper. Add a single layer of beef cubes to the stock pot (or Dutch oven if using) - work in batches so you don’t crowd the pan. Sear the beef until browned on all sides. Transfer the seared beef to the plate with the bacon and continue searing until all the beef is browned and transferred to the plate. Set aside.
Add the carrots and onion to the same pot over medium heat (there should be some fat left in the pan; if not add a little olive oil so the vegetables don’t burn). Cook until the onions are lightly browned, stirring occasionally. Add the garlic and cook for 1 minute.
Add the Cognac and simmer until the liquid is almost completely gone (this just takes a minute so stay close). Return the beef and bacon to the pan with any accumulated juices on the plate. Add the wine and enough beef broth to almost cover the meat (don’t fully submerge the beef in liquid). Add the tomato paste and thyme. Bring to a simmer, cover with a tight-fitting lid and place the pot in the oven for 75 to 90 minutes, until the meat and vegetables are very tender when pierced with a fork.
Combine 2 tablespoons of the butter and the flour and mash with a fork until blended. Add the mixture to the pot. Add the frozen onions and bring to a simmer. Simmer while you cook the mushrooms.
Melt the remaining 2 tablespoons of butter in a medium skillet over medium heat. Add the mushrooms and cook for 5 to 6 minutes, until soft. Add the mushrooms to the pot. Season to taste with salt and pepper.
To toast the bread, preheat the oven to 400 degrees.
Brush both sides of the bread slices with olive oil and transfer the slices to a baking sheet. Bake for 5 to 6 minutes, turning once, until golden and crisp. Rub one side of each slice with the cut garlic clove.
Garnish the stew with the parsley. Serve the stew with the bread slices on the side.