Turn the Instant Pot (or similar electric pressure cooker) to sauté. Add the butter and let melt. Once melted, add the onions, garlic, thyme, and bay leaf and stir to combine. Cook, stirring, until onions slightly soften and start to release liquid, about 5 minutes. Stir in 3 tablespoons water. Cover and seal the Instant Pot, then set to cook on HIGH pressure (manual setting) for 20 minutes. Release pressure to vent immediately.

Remove the lid, then turn the Instant Pot back to sauté. Cook for 5 minutes until some of the liquid evaporates, then add the wine and bring to a simmer, scraping up any brown bits that have collected on the bottom of the pot. Let simmer for 10 minutes, until most of the wine has evaporated. Discard the thyme stems and bay leaf.

Add the bone broth and stock. Bring to a simmer and let cook until the soup thickens, about 10 minutes. Add the salt and pepper, then taste and adjust the seasonings as needed.

When you’re ready to serve, prepare the crouton topping. Preheat your oven's broiler. Arrange the baguette slices on a baking sheet in a single layer. Sprinkle the slices with the Gruyère. Broil until bubbly and golden brown, 3 to 5 minutes, watching constantly towards the end so that the bread does not burn. Remove promptly. (See notes section for alternate serving method)

Ladle the soup into bowls, then carefully float the toasted cheese baguettes on top. Enjoy!