In a large pot, heat a splash of olive oil over medium heat. Add chopped yellow onion, diced carrots, and celery sticks, stirring occasionally until the vegetables soften and the onion becomes translucent, about 5–7 minutes.

Pour in the chicken or vegetable broth and drop in a parmesan rind for extra richness. Bring the mixture to a gentle boil over high heat, then reduce the heat to low. Cover the pot and let it simmer for 15-18 minutes until the vegetables are tender.

Remove the pot from heat and carefully take out the parmesan rind. Use an immersion blender to purée the soup directly in the pot, or transfer the vegetables and some broth to a blender. Blend until smooth.

Return the puréed mixture to the pot and bring it back to a simmer over medium heat. Stir in the pastina pasta, letting it cook uncovered for about 7-9 minutes, or until al dente.

Once the pastina is cooked, season your soup with salt and pepper to taste. Ladle the soup into bowls and garnish generously with grated parmesan cheese and fresh parsley.