In a small soup pot over medium-low heat, melt the butter. When the butter is melted, whisk in the flour, sugar, salt, pimentón, and piment d’Espelette. Cook, whisking constantly, until the mixture has a nutty, savory aroma, about 3 minutes.
Whisk the strained tomatoes, chicken stock, and vinegar into the butter mixture until smooth. Raise the heat to bring to a simmer, stirring occasionally, and simmer gently for about 5 minutes.
Ladle the soup into bowls, garnish with a dollop of crème fraiche, and serve immediately.