Preheat the oven to 400˚. Line a baking sheet with parchment paper or a silicone mat.
Combine the drained whole tomatoes, olive oil, brown sugar, carrots and shallots in a large bowl and toss to coat. Season with salt and pepper. Spread the vegetables on the baking sheet and roast until caramelized, about 30 minutes.
Heat a soup pot over medium heat. Add the butter and cook until foaming. Add the red pepper flakes and garlic and sauté for 1 minute. Add the tomato paste and cook, stirring, 1 to 2 minutes, then add the sherry. Cook until all the liquid has evaporated and the alcohol has cooked off, 1 to 2 minutes. Add the roasted vegetables, crushed tomatoes and 1 cup chicken stock. Season with salt and pepper, bring to a simmer and cook 15 minutes.
Working in small batches, transfer the soup to a blender and puree until smooth. Return to the pot and add more chicken stock to adjust the consistency to how you like it. Taste again and adjust the seasoning with salt and pepper. Ladle into bowls and top with croutons.