Heat 2 tablespoons of olive oil in a large heavy-based saucepan. Fry the red pepper, onion and garlic in the pan for 10-15 minutes over medium heat, stirring often.
Add the tinned tomatoes, smoked paprika, sugar and stock. Season with salt and freshly ground pepper. Bring to the boil, reduce heat, cover and simmer for 15 minutes.
Blend the soup with a hand blender or in a jug blender until smooth. Cool, cover and chill.
Meanwhile, make the anchovy butter for the crostini. In a pestle and mortar pound the anchovy fillets into a paste. Mix in the butter and lemon juice, blending thoroughly. Season with freshly ground pepper and mix in the parsley. Cover and chill until use.
Just before serving prepare the crostini. Drizzle each slice of sourdough bread with half a tablespoon of olive oil.
Grill the bread until lightly toasted. Spread each slice generously with the anchovy butter.
Ladle the soup into 4 serving bowls. Top with a dollop of creme fraiche and a few basil leaves. Serve with the anchovy crostini on the side.