Put the spinach in a large wide pan and cook over a medium heat for 5 minutes until piping hot. Tip into a colander set over a bowl and press with the back of a spoon to get rid of any excess moisture. Set aside.
Heat the oil in a large non-stick frying pan, add the garlic and cook over a low heat for 2 minutes making sure it doesn’t catch. Return the spinach to the pan and stir in the crème fraîche and Gruyère. Season with pepper and serve.