Preparation: Begin by preparing all your ingredients. Chop the onion roughly and peel and dice the potato. Mince the garlic.
Sauté the Vegetables: Heat the oil in a large pot over medium heat. Once hot, add the chopped onion and sauté for about 5 minutes until it becomes translucent. Add the minced garlic and cook for another minute until fragrant.
Add the Potatoes: Add the diced potatoes to the pot, stirring to combine with the onion and garlic. Cook for about 3-4 minutes to let the potatoes start to soften.
Add Spinach and Peas: Add the spinach leaves to the pot, stirring them in until they wilt. This should take about 2 minutes. Once the spinach has wilted, add the peas. If using fresh peas, ensure they are rinsed; if using frozen peas, they can go in directly from the freezer.
Add Broth and Simmer: Pour in the chicken broth, making sure it just covers the vegetables. You may need a bit more or less broth depending on the size of your pot and the amount of vegetables.
Season with a pinch of salt and pepper. Bring the mixture to a boil, then reduce the heat to medium-low, cover, and let it simmer for about 10 minutes, or until the potatoes are tender.
Blend the Soup: Once the vegetables are cooked, use an immersion blender to blend the soup directly in the pot until smooth. If you don't have an immersion blender, carefully transfer the soup in batches to a regular blender and blend until smooth, then return it to the pot.
Adjust Seasoning and Consistency: Taste the soup and adjust the seasoning with more salt and pepper if needed. If the soup is too thick for your liking, you can add a bit more broth to thin it out.
Serve: Ladle the soup into bowls. Top each serving with a handful of croutons and a sprinkle of grated Parmesan cheese.