Heat a large dutch oven or heavy skillet to medium-high. Add bacon pieces and cook until the bacon is crispy and has rendered its fat, stirring occasionally. This should take about 5-7 minutes. Remove bacon from pan with a slotted spoon and set aside on a paper towel to drain. Discard about half of the bacon fat and add 2 tablespoons of olive oil. Keep the skillet on the stove and do not turn down the heat.

Dredge the beef pieces on all sides in the flour and shake to remove excess flour. Add beef to the pan and sear on all sides, turning with your kitchen tongs about every two minutes. You may have to do this in batches; make sure not to overcrowd the pan as it will halt the searing process. Once beef is browned, remove, season with salt and pepper and set aside.

Turn the pan down to medium and add remaining tablespoon of oil and butter. Add onion slices, carrots and mushrooms. Sauté until onions become fragrant and begin to brown on the edges and mushrooms begin to release their water, about 5-7 minutes. Add garlic and tomato paste and cook for one minute more. Turn the heat to high. Deglaze the pan with the red wine making sure to scrape up all the brown bits from the bottom of the pan with a wooden spoon. Allow wine to reduce by about half before removing from heat and adding to your slow cooker.

Add beef pieces, stock, bay leaf, bacon and herb bouquet to slow cooker along with the vegetable mixture. At this point, you can refrigerate the stew for up to a day before cooking on low for 8 hours. Or, you can cook immediately. Stir in the pearl onions the last 30 minutes of cooking. Season with salt and pepper to taste before serving.