Preheat your oven to 400°F (200°C).
On a large sheet pan, arrange the cherry tomatoes, halved Roma tomatoes, quartered onions, and garlic cloves (tops cut off).
Drizzle with olive oil and sprinkle with fresh thyme, rosemary, oregano, salt, and pepper.
Roast in the oven for 30-40 minutes, until the tomatoes are soft and caramelized.
Remove the garlic cloves from their skins and transfer all the roasted vegetables and herbs to a blender or large pot.
Add vegetable broth, freshly grated Parmesan cheese, and milk.
Blend until smooth, then transfer to a pot and heat gently on the stove until warmed through.
Adjust seasoning with salt and pepper as needed.