Turn your oven on to 180 degrees celsius for a fan oven or 200 degrees celsius for a conventional oven. Line a 1kg (or 2lb) loaf tin with baking parchment. Place a large glass bowl in a saucepan containing a cup of water. The bowl should be above the water, not touching it. When the water is simmering, place the chocolate, chopped into small pieces, in the bowl to melt. Stir frequently with a wooden spoon. Once the chocolate has melted take off the heat and place to one side to cool.