Dice the onions into small uniform pieces and mince the garlic. Set aside.
Set the Instant Pot to sauté mode. Melt the butter in the pot, and add the olive oil. When melted, add the diced onions, garlic, thyme, and bay leaf. Stir to combine.
Sauté, continue to stir until the onions become soft and release liquid, about 5 minutes. Add water, and then cover and seal the Instant Pot. Set the Instant Pot to Sealing Position and cook on Manual High Pressure for 20 minutes. Carefully set your Instant Pot to Venting Position to allow for a Quick Release once the Instant Pot is finished cooking.
Remove the lid, and set the Instant Pot back to sauté mode. Pour in the wine, and bring to a simmer. Simmer the wine for about 10 minutes, or until most of the wine has evaporated. Once done simmering, remove the thyme and bay leaf with a slotted spoon.
Next, add both the beef and chicken stock. Bring the soup back to a simmer and cook for an additional 10-15 minutes or until the soup slightly thickens. Add salt and pepper, to taste.
Preheat the oven broiler. Slice the baguette into slices, and then place the baguette slices onto a baking sheet. Sprinkle each baguette with cheese. Place the baguette slices into the oven and broil until cheese is melted and golden brown, about 3 to 5 minutes.
Ladle the French onion soup into bowls, then place slices of the cheesy bread directly in the bowl to float on top of the soup. Serve immediately.
Prepare your Instant Pot French Onion soup even quicker by learning how to dice an onion perfectly in seconds.
Gruyère may be traditional for French Onion soup, but feel free to experiment with different types of cheese. Great alternatives include Fontina, Gouda, sharp cheddar, and Swiss cheese.
If you own ovenproof bowls and prefer to broil your baguette slices directly on top of the soup, feel free to do so. Place the ovenproof bowls on a baking sheet and place under the broiler for about 3-5 minutes.