Preheat oven to 375 F. Halve tomatoes and place skin side down on a baking sheet lined with aluminum foil. Add unpeeled garlic to pan. Drizzle tomatoes and garlic with 2 Tbsp olive oil, coarse salt and black pepper. Roast for 45 minutes, remove garlic from pan and set aside to cool. Continue roasting tomatoes for 15-30 more minutes until the underside skin is browned.

Meanwhile, heat remaining olive oil in a large saucepan over medium heat. Add chopped onion and cook until soft and translucent, about 5-7 minutes.

Peel roasted garlic and add it to the pan with onions along with the tomatoes and stock. The stock should just cover the tomatoes. Add 1 Tbsp balsamic vinegar. Use an immersion blender to puree until smooth.

Serve with croutons and parmesan garnish, alongside fancy pants grilled cheese sandwiches for maximum fancy pants effect.