Preheat the oven to 425 degrees.
Place the sliced tomatoes and garlic cloves on the sheet pan and toss in a light coating of olive oil.
Roast tomatoes for 30 to 45 minutes. Tomatoes are ready when the skins begin to blacken and pull away from the tomato flesh.
While tomatoes are in the oven, heat butter in the stock pot over medium heat.
Add diced onions and sauté until soft.
Pour chicken broth into the stockpot and season with salt, pepper, and basil. Add the roasted red peppers.
Remove tomatoes from the oven and allow to rest at room temperature for a few minutes. Using a tongs, peel the skins from the tomatoes and discard.
Add the tomatoes to the stockpot and stir.
Using the immersion blender, puree the sauteed onions, roasted tomatoes, garlic, and roasted red peppers.
Allow the soup to simmer for about 20 minutes.
Serve with fresh baked croutons and shredded cheddar cheese.