Turn your electric pressure cooker to the sauté mode. Melt your butter and then add the onions, garlic, thyme, and bay leaf, stir to combine. Sauté the onions for about 5 minutes until they start to release water. Stir in 3 tablespoons water. Secure the lid to your pressure cooker, seal the valve and cook on HIGH pressure (manual setting) for 20 minutes. Once the timer has counted all the way down release the pressure to vent.
Remove the lid, then turn your pressure cooker back to the sauté mode. Cook your onions for about 5 - 8 more minutes until some of the extra liquid evaporates. Add the sherry and to bring to a simmer. Be sure to scrape up any brown bits on the bottom of the pot, it gives the soup a little more flavor. Let simmer for 10 minutes, until most of the sherry has evaporated. Discard the bay leaf.
Add the vegetable broth and bring to a simmer. Cook for an additional 10 minutes or so until your soup has thickened. Finish with salt and pepper to taste.
Preheat your broiler. Arrange ovenproof bowls on a sheet pan and ladle in your soup. Float a slice or two of the baguette slices on top of the broth and cover with a slice of cheese. Broil until bubbly and golden brown, 3 to 5 minutes.