Preheat oven to 400°F. Wrap garlic cloves in a tight foil packet. Spread out the halved tomatoes and onion onto a large baking sheet, seasoning with salt and pepper. Drizzle the tomatoes with olive oil. Add foil packet of garlic to tray. Roast about 1 hour.
After roasting, unwrap garlic packet and peel cloves. Transfer tomatoes, any juices, garlic cloves, and onion to a blender and blend until smooth. Strain through a sieve for a smoother texture if desired. Over medium high heat, cook 2 tbsp tomato paste with a bit of olive oil, stirring frequently, until color deepens and caramelizes. Transfer puree to the pot and add thyme, crushed red pepper and stock, and bring to a boil. Reduce heat to a simmer for 25 minutes. Remove from heat and adjust seasonings to taste.
To serve soup, swirl in some heavy cream and finish off with chopped chives, freshly ground black pepper, and sharp cheddar granola.