Preheat the oven to 400 degrees F. Line a baking sheet with a silicone baking mat or parchment paper.
Combine the tomatoes, olive oil, light brown sugar, carrots, shallots, garlic, dry sherry and some salt and pepper in a mixing bowl and toss to coat. Place the vegetables on the prepared baking sheet and roast until caramelized, 30 to 40 minutes.
Heat a cast-iron Dutch oven or large pot over medium heat. Add the butter and cook until foaming. Add the crushed red pepper if using and the tomato paste and cook for 1 to 2 minutes. Add the roasted vegetables and chicken stock. Bring to a boil and then lower to a simmer. Let simmer for 15 minutes.
Using an immersion blender, puree the soup until uniform in texture with a slightly thick consistency. Stir in the heavy cream. For a smoother texture, transfer to a standard blender and puree until smooth. Taste and season if necessary. Serve and garnish with basil leaves and crushed black pepper.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.