Preheat oven to 400F. Line a large baking sheet pan with parchment paper and arrange tomatoes, peppers, and garlic on pan. Drizzle olive oil over top and season tomatoes and peppers well with salt and pepper.
Roast tomatoes and peppers at 400F 25-30 minutes until tomatoes and peppers are very soft and juicy. Allow to cool several minutes, then peel skin from garlic, rub skins from peppers and tomatoes and discard.
Pour peeled tomatoes, sweet pepper, garlic, and any accumulated juices into a blender (alternatively you can use a handheld immersion blender in a pot) Blend on high speed until smooth. Pour into a Dutch oven or medium pot.
Whisk tomato paste into soup and bring to a simmer over medium-high heat, stirring occasionally until tomato paste is incorporated into soup. Reduce heat to medium and add milk, cream, oregano, and sugar, folding soup until combined. Cook an additional 5 minutes on medium until soup is heated through.
Season soup with salt and pepper to taste if needed and stir in basil. Serve warm with croutons and additional fresh basil on top of individual bowls if desired. Enjoy!