Preheat oven to 450 F.  Lightly wash and slice heirloom tomatoes in half.  Cut the top off of the garlic head and drizzle with olive oil.  Wrap garlic in foil.  Place tomatoes and garlic on the baking sheet and drizzle with 1/4 cup olive oil.  Sprinkle with salt and pepper.  Roast in the oven for 20-30 minutes or until tomatoes begin to caramelize.  Remove from oven.

Slice onion and in a large stock pot on the stove over medium heat, cook onion with 3 tbl olive oil until onions caramelize, about 10 minutes.

Add stock, bay leaf and butter. Add roasted tomatoes and garlic.

Bring to a boil, reduce heat and simmer for 15 to 20 minutes or until liquid has reduced by a third.

Remove the bay leaves and thyme and using an immersion blender, blend until smooth.

Return soup to low heat and add basil, grated parmesan, and salt and pepper to taste.