Remove any bones from the tuna. Put the tuna into a food processor or blender, together with the anchovies, 225 ml (8 fl oz) 1 cup of the olive oil and the flat leaf parsley. Process until the sauce is very smooth.

Spoon the creme fraiche into the food processor or blender and process again for a few seconds to blend thoroughly. Season with salt and pepper to taste.

Bring a large pan of lightly salted water to the boil. Add the spaghetti and the remaining olive oil and cook for 8 - 10 minutes until tender, but still firm to the bite.

Drain the spaghetti, return to the pan if and place over a medium heat. Add the butter and toss well to coat. Spoon in the sauce and quickly toss into the spaghetti, using 2 forks.

Remove the pan from the heat and divide the spaghetti between 4 warm individual serving plates. Garnish with the olives and serve immediately with warm, crusty bread.

If liked, you could add 1 - 2 garlic cloves to the sauce, substitute 25 g (1 oz) 1/2 cup chopped fresh basil for half the parsley and garnish with capers instead of black olives.