Wash and peel the vegetables. Dice the onion, carrots, celery, and potato into small, even pieces. Mince the garlic finely.
In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for 3-4 minutes until translucent. Stir in the minced garlic and cook for another minute.
Add the diced carrots, celery, and potato to the pot. Sauté these vegetables for about 5 minutes, stirring occasionally.
Pour in the vegetable broth. Add the frozen peas and corn kernels, along with the dried thyme, rosemary, salt, and black pepper. Stir everything together and bring to a boil, then reduce the heat and let it simmer for 15-20 minutes.
In a small bowl, whisk together the heavy cream and flour until smooth. Gradually add this mixture to the soup, stirring continuously to avoid lumps. Allow the soup to simmer for an additional 5 minutes until it thickens slightly.