Toss the garlic cloves with one tablespoon of oil in a saucepan, cover with greaseproof paper and cook on a low heat for a couple of minutes. Remove the garlic from the pan and cover with cling film. Set aside. Season the lamb generously with salt and pepper. In a heavy frying pan, heat the oil until nearly smoking. Add the lamb, and cook over high heat until well browned. This should take about 10 minutes, by which time the lamb will be about medium rare.
Remove the lamb and the garlic to a warm plate, and cover with foil. Pour off the fat from the pan, and add the wine, or water. Scrape the caramelised juices off the bottom of the pan as the liquid boils. Now add the cream, and bring to a fast boil. Squeeze the garlic from their skins. They should pop out easily. Mash lightly with a fork. Add the cream and the garlic to the pan, bring to a fast boil, then remove from the heat, and stir in the basil, and the mustard.
To serve, slice the lamb, adding any juices to the sauce. Arrange on a warm plate with a little sautéed spinach. Spoon the sauce around.