Bring about an inch of water to a simmer in your saucepan. Set the heatproof bowl in the mouth of the pot, making sure the water doesn't touch the bottom of the bowl. Stir chocolate occasionally as it softens. When you have just a few small unmelted chunks, remove bowl from heat (leftover heat will melt the rest).
Place some baking paper on a baking tray and pour melted chocolate, using a spatula spread chocolate until roughly a few millimetres think.