1.1. Preheat the oven to 350° F. Toss the bread cubes in a large bowl with 2 tablespoons of the olive oil. Place on a baking sheet and toast in the oven for 15 minutes, or until crisp, shaking periodically. Set aside to cool.
2.2. Heat the remaining 2 tablespoons olive oil in the pressure cooker over medium-high heat. Add the onions and garlic. Cook for 5 minutes. Add the thyme, dry sherry, and 2 cups of stock.
3.3. Cover and bring to high pressure over high heat. Lower the heat to stabilize the pressure. Cook for 6 minutes.
4.4. Remove from the heat. Let the pressure release by using the quick release method (click link below for instructions if you are unfamiliar with working with Pressure Cookers).
5.5. Unlock and remove the pressure cooker cover.
6.6. Preheat the broiler. Add the remaining 2 cups of stock and bring to a simmer. Season with salt and pepper.
7.7. Ladle the soup into heatproof bowls. Float some bread cubes on top and sprinkle with the grated cheese. Place the soup bowls on a baking pan and set under the broiler until the cheese melts and is bubbly, about 1 to 3 minutes, depending on your broiler.