1. Heat olive oil in a saucepan over medium heat.
2. Add chopped onions, carrots, and celery. Sauté until softened, about 10 minutes.
3. Stir in tomato paste and cook for another 5 minutes.
4. Sprinkle flour over the vegetables and stir well to combine. Cook for 2 minutes.
5. Gradually add vegetable broth, whisking constantly to avoid lumps.
6. Add soy sauce, thyme, rosemary, salt, and black pepper. Bring to a boil.
7. Reduce heat and let it simmer for 45 minutes, stirring occasionally.
8. Strain the sauce through a fine-mesh sieve. Serve warm.