Cook the spaghetti in a large saucepan of salted boiling water, adding the olive oil, for 8 - 10 minutes or until tender. Drain the spaghetti in a colander and return to the pan. Add the butter, toss thoroughly to coat and keep warm until required.

Remove any bones from the tuna and flake into smaller pieces, using 2 forks. Put the tuna in a blender or food processor with the anchovies, olive oil and parsley and process until the sauce is smooth. Pour in the creme fraiche and process for a few seconds to blend. Taste the sauce and season with salt and pepper.

Warm 4 plates. Shake the saucepan of spaghetti over a medium heat for a few minutes or until it is thoroughly warmed through.

Pour the sauce over the spaghetti and toss quickly, using 2 forks. Serve immediately with a small dish of black olives, if liked.