Step 1: Prepare all vegetables by washing and cutting the eggplant, zucchini, and bell peppers into roughly 1-inch cubes. Dice the onion and mince the garlic.
Step 2: In a large heavy-bottomed pot or Dutch oven, heat about 1-2 tablespoons of olive oil over medium-high heat. Add the cubed eggplant in a single layer (work in batches if necessary to avoid crowding the pan). Cook, stirring occasionally, until softened and lightly browned, about 5-7 minutes. Remove with a slotted spoon and set aside.
Step 3: Add a little more olive oil to the pot if needed, then add the zucchini. Cook until lightly browned and tender-crisp, about 4-6 minutes. Remove and set aside with the eggplant.
Step 4: Repeat with the bell peppers, cooking until slightly softened, about 3-5 minutes. Remove and set aside with the other vegetables.
Step 5: Reduce the heat to medium. Add the diced onion to the pot and cook, stirring frequently, until translucent and softened, about 5-7 minutes. Add the minced garlic and cook for another minute until fragrant.
Step 6: Stir in the crushed tomatoes, tomato paste, vegetable broth, Herbs de Provence, and bay leaf. Bring the mixture to a gentle simmer, stirring to combine all ingredients.
Step 7: Gently fold the reserved cooked eggplant, zucchini, and bell peppers into the tomato sauce. Add the chopped fresh basil. Stir gently to coat all vegetables.
Step 8: Reduce the heat to low, cover the pot, and simmer for at least 30-45 minutes, or up to 1.5 hours, stirring occasionally. The longer it simmers, the more the flavors will meld and deepen. The vegetables should be very tender but still hold their shape.
Step 9: Remove the bay leaf. Taste and adjust seasoning with salt and freshly ground black pepper as needed.
Step 10: Serve warm, garnished with extra fresh basil, as a main course or a delicious side dish. This ratatouille recipe tastes even better the next day!