Slice the bacon into strips then saute in the Instant Pot (set to Saute mode) until crisp and golden. Remove and set aside.
Pat the beef dry with paper towels (this will allow the beef to brown nicely) and season with salt and pepper. Brown the beef in the IP in batches.
While the beef is browning, peel and slice the carrots, chop the onion and crush the garlic.
Remove the browned beef from the IP and add the onion, carrots, thyme and bay leaf.
Cook for a few minutes until fragrant then add the garlic.
Saute for a minute then sprinkle in the flour. Stir to coat the vegetables then pour in the wine and add the tomato paste.
Bring to a simmer then add the beef and bacon back into the pot and top with the stock. Season with salt and pepper then secure the lid of the Instant Pot, making sure the vent is set to sealing position.
Cook the Boeuf Bourguignon for 45 minutes on high pressure.
Quick release the pressure after 45 minutes.
Make sure the beef is tender, if not, cook for another 10-15 minutes on high pressure.
Add the mushrooms and test the seasoning. Adjust if necessary.
Secure the lid and cook on high pressure for another 5 minutes.
Quick release the pressure, season to taste and serve with mashed potatoes.