Melt the butter with olive oil in your pressure cooker over medium heat. You wanna get it nice and hot before adding the onions.
Throw in the sliced onions and cook, stirring often, until they’re caramelized. This takes about 25 minutes with slow release flavor development, but pressure cooker helps speed it up plenty.
Pour in beef broth, dry sherry, and sprinkle in dried thyme. Stir well and add salt and pepper to taste.
Seal the lid with your pressure cooker's sealing ring and set it to cook until the soup is rich and bubbly. Use slow release after pressure cooking to keep flavors mellow.
While that’s happening, preheat your oven broiler to get ready for that cheesy toast on top.
Pop the French bread slices on a baking sheet and under the broiler until lightly browned on each side. You want some crunch but not burnt.
Ladle the soup into oven-safe bowls, top each with toasted bread, add a slice of provolone, then sprinkle diced Swiss and Parmesan.
Broil just until the cheese bubbles and turns golden, about 2 to 3 minutes.
Then you’re dang ready to dig in!
Notes
Cool completely before storing. Keep in airtight containers in the refrigerator up to 4 days or freeze without bread for up to 3 months. Reheat gently on the stove.