Line a baking pan with parchment paper.
Wash the tomatoes and peppers. Peel garlic cloves and the onion. Dice the onion to small cubes.
Cut the tomatoes into 6 wedges and arrange on the baking sheet. Toss the garlic cloves throughout the tomatoes. Drizzle with about 2 Tbsp of olive oil. Place in a preheated to 425 oven for about 20 -25 minutes, or until the tomatoes are well roasted with some charring on tops.
Roast the pepper on the grill over medium heat, rotating on all sides until well softened and good grill marks develop. This step can be possibly omitted, instead just toss the cut up pepper with the tomatoes and roast together.
Add 3-4 tablespoons of oil to a skillet and heat over medium heat. Add the diced onion, then stirring periodically sauté until golden in color. Remove the caramelized onions to a separate bowl with only 2 tablespoons of oil. Discard or repurpose the rest of the oil.
To a blender add the roasted tomatoes and garlic, grilled pepper, sautéed onions with the oil, black pepper, salt, sugar, cayenne pepper, Italian seasoning, or basil and puree on high speed until completely smooth, about 2 minutes.
While continuing to blend, through the opening in the lid pour 1.5 cups of chicken broth, then 1/4 cup of heavy cream and taste for seasoning. Add another 1/2 cup of chicken broth for thinner consistency.