Instant Pot French Onion Soup

Select SAUTÉ setting on a programmable pressure multicooker (such as Instant Pot). (Times, instructions, and settings may vary according to cooker brand or model.) Select HIGH temperature setting, and allow to preheat 2 to 3 minutes. Add butter to cooker, and stir to melt. Add onions, thyme, rosemary, and 1/2 teaspoon of the salt to cooker. Cook, stirring constantly, until onions are coated with butter. Once coated, cover cooker with a saucepan lid or glass pie plate. Let onions steam until softened, but not browned, about 10 minutes. Uncover and continue to cook, stirring often, until onions are a deep golden brown, about 20 more minutes. 

Add vermouth and vinegar; cook, stirring constantly and scraping to loosen any browned bits from bottom of cooker, until liquid is reduced by half, about 1 minute. Stir in broth, Worcestershire, mustard, pepper, bay leaf, and remaining 1/2 teaspoon salt. Press CANCEL.

Cover cooker with lid, and lock in place. Turn steam release handle to SEALING position. Select MANUAL/PRESSURE COOK setting. Select HIGH pressure for 5 minutes. (It will take 10 to 15 minutes for cooker to come up to pressure before cooking begins.) Preheat oven to broil with oven rack about 6 to 8 inches from heat.

When cooking has finished, let the pressure release naturally (float valve will drop). (This will take 10 to 15 minutes.) Remove lid from cooker. Ladle soup into broiler-safe bowls, leaving a 1/2 inch of space at the top, and place bowls on an aluminum foil-lined baking sheet. Top each bowl with a baguette slice, and sprinkle each with 1/4 cup shredded cheese. Broil until cheese is melted and bubbly, about 2 minutes. Garnish with additional black pepper. Serve immediately.