Preheat your oven to 275°F (135°C). Line a baking sheet with parchment paper for easy cleanup.
Place halved tomatoes, cut side up, on the prepared baking sheet in a single layer.
Drizzle tomatoes with olive oil and balsamic vinegar (if using). Sprinkle evenly with garlic, salt, and pepper.
Bake for 2–2½ hours until the tomatoes begin to caramelize around the edges and shrink slightly. They should look soft and wrinkled, but not burnt.
Remove from the oven and let cool slightly. Toss gently with fresh basil just before serving.
