Position rack in oven to place Dutch oven in the center for baking and adding another top rack for baking croutons.
Preheat oven to 425°.
Measure all ingredients.
Add can of whole or crushed tomatoes to the Dutch oven, breaking tomatoes up a bit.
Mix in minced garlic, chopped onion, 2 T butter, olive oil, salt, pepper and add thyme sprigs on the top.
Add the Dutch oven to the oven, uncovered, and roast for about 45 minutes.
While the tomatoes are roasting, cut or tear the crusty bread into 1" crouton sized pieces and add to a bowl. Pour over melted butter and Italian seasoning and stir to coat.
Line a baking sheet with sides and add the croutons in an even layer.
Add to the upper rack of the oven and bake until toasty--about 10-25 minutes.
Remove croutons from the oven and set aside.
While croutons and soup are in the oven, grate both cheeses.
When tomatoes are finished roasting, move them to the stovetop and remove the thyme sprigs, if desired. Add in the vegetable broth and simmer for about 10 minutes to warm broth into the mixture.
Stir the balsamic vinegar into the soup.
Remove from heat.
Use an immersion blender, or use a VitaMix if you have one, until the soup is a smooth consistency. Taste and add more salt, if needed.
Add a layer of the grated Cheddar cheese over the soup. See tip below: If adding to the entire pot of soup, add half. If adding to individual serving bowls, add an even layer. Top with the layer of crusty croutons.
Finish with the remaining half of the grated Cheddar cheese for the entire pot or even layer in individual bowls and then the grated Parmesan cheese.
Turn the broiler to high and add the Dutch oven close to the broiler until the cheese melts.
Remove from the oven and serve immediately.
ENTERTAINING TIP: For perfect entertaining, add the soup to broiler safe soup dishes before topping with the cheese and croutons. Perfect proportion of grilled cheese goodness to soup every time!When filling individual serving bowls for the broiler, don't forget to allow room for the grilled cheese topping AND place on a baking sheet with sides to catch the overflow. Parchment paper beneath them helps with clean up!MAKE SURE that those soup dishes are BROILER SAFE!