• In a large soup pot, heat olive oil over medium-high heat.
• Add onion, leeks, carrots, and garlic, season with salt, and cook about 7-10 minutes, until the vegetables begin to soften.
• Add vegetable broth and bring to a boil.
• Reduce heat to medium-low and let simmer for 20 minutes.
• Puree with an immersion blender or in a blender.

Make the grilled cheese croutons:

• Brush one side of each slice of bread with olive oil.
• Place two mozzarella slices each on two slices of bread, then top each piece with remaining bread to make two sandwiches.
• Heat cast iron skillet (or any kind of skillet will work) over medium heat.
• Cook sandwiches 4-5 minutes on each side, until golden and cheese has melted.
• Let cool slightly, then cut into crouton-sized pieces.
• Top each bowl of soup with croutons and fresh herbs.
• Serve and enjoy!