For the soup

1. In a large pot or Dutch oven, heat the olive oil over medium heat.  Add the onions and cook on medium-low heat for 15 minutes, stirring occasionally, until golden brown.  Add the garlic and cook one more minute.
2. Stir in the stock, tomatoes, 2 teaspoons salt, 1 teaspoon pepper, and 1 teaspoon basil. Bring the soup to a boil, then lower the heat and simmer for 15 minutes.
3. Remove the soup from the heat.  Transfer the soup, in batches if necessary, to a blender and blend until smooth  (or use an immersion blender).  Return soup to the pot.

For the grilled cheese croutons

1. Preheat a skillet over medium heat.
2. Generously butter one side of a slice of bread. Place bread butter-side-down onto skillet bottom and add 1-2 slices of cheese. Butter a second slice of bread on one side and place butter-side-up on top of sandwich. Grill until lightly browned and flip over; continue grilling until cheese is melted. Repeat with remaining 2 slices of bread, butter and slices of cheese.
3. Cut the grilled cheese sandwiches into 1-inch cubes and serve in the bowls of soup. Enjoy!