Preheat the oven to 400 degrees F.
Place the halved tomatoes and quartered onion on a large baking sheet. Slice the top off the garlic bulb to expose the cloves.
Drizzle the tomatoes, onion, and garlic with olive oil, then sprinkle with the Italian seasoning, salt, pepper, and chili flakes. Wrap the garlic bulb loosely in foil and set it on the pan.
Roast for 35 to 40 minutes, until the tomatoes and onion are soft and caramelized.
Squeeze the roasted garlic cloves out of their skins into a blender. Add the roasted tomatoes and onion along with any pan juices.
Add the broth and cottage cheese and blend until smooth and creamy.
Pour into a pot and warm over medium heat, stirring, until hot. Taste and adjust the seasoning.
Serve warm with your favorite toppings.