Preheat oven to 350 degrees. Heat your Dutch oven with the oil over medium low heat. Add the pancetta. Cook till it’s browned. Use a screen cover to keep the oil from splattering your stovetop. When browned, remove with a slotted spoon and set to the side.
Dry the beef with a paper towel. Season with kosher salt and fresh ground pepper. In three separate batches, brown the beef in the Dutch oven (don’t let the beef cubes touch), setting the browned cubed on a plate.
In the same Dutch oven, add the carrots, onions and season with salt & pepper. Sauté for 10-15 minutes. Add the garlic and sauté for an additional 2-3 minutes.
Add the beef (and the juices) and the pancetta to the Dutch oven. Sprinkle with the flour. Stir to incorporate. Continue stirring for an additional four minutes. The bottom and sides will brown.
Slowly add the wine, scraping the bottom and sides of the pan to remove the browning. This will take a while, but as you keep adding wine the browning will lift. Add the beef stock, tomato paste, thyme and bay leaf. Bring to a simmer. Place in the oven (on the bottom third of the oven) and cook for 2 ½ hours.
Cut the root end off of each onion (be careful not to cut off to far into the onion). Put in a small saucepan and cover with cold water. Add a generous pinch of salt. Bring to a boil. As soon as it starts to boil, drain in small colander and rinse with cold water. Pinch the outer skin off and set the onion aside or refrigerate overnight.
Use a paper towel or mushroom brush and remove any dirt from the mushrooms. Cut the tough end of the mushroom stem off. Slice the mushrooms. In a sauté large pan, heat butter and oil. You want to give your mushrooms lots of room so they don’t get overcrowded and steam. Once the butter/oil is hot, add the mushrooms. Saute for 8-10 minutes or until golden brown and all the juices have absorbed. Set to the side or refrigerate overnight.
At this point you can cool to reheat the next day or continue on…
If reheating, warm the Bourguignon on a low heat to s slow simmer. Add a couple cups of water if the Bourguignon is too thick. Add the onions and mushrooms and continue cooking for an additional 30 minutes.
Serve over potatoes with warm bread on the side.