Start by peeling the onions, then thinly slicing them from root to stem. You should have about 10 cups of sliced onions in total.
To caramelize the onions, begin by melting the butter in a 5 to 6 quart pot over medium heat. Add the onions and toss them around so they're coated in the butter.
Cook the onions on medium heat, occasionally stirring, until they have softened (about 15 to 20 minutes).
Add sugar, salt, garlic powder, and pepper to the pot. Cook frequently stirring for 510-15 minutes or until onions caramelize. Stir in wine; cook for 1 minute or just until it evaporates.
To the Instant Pot, add beef broth and caramelized onions.
Close the lid securely and move the pressure release valve to the "Sealing" position. Press either "Manual" or "Pressure Cook," then cook at high pressure for 5 minutes.
After cooking, press "Cancel" and use the quick release. Then, preheat the broiler.
Serve the soup in individual ovenproof bowls, topping each with 1 or 2 slices of bread and cheese. Place the bowls on a large baking sheet and broil them for 3-4 minutes, until the bread is toasted and the cheese is melted and browned.