Get a large baking sheet cover it with baking parchment and place to one side.
Heat your oil in a medium sized pan until it is sizzling, add your popcorn kernels and cover your pan with a lid. Shake the pan lightly over the heat until the popping has almost come to a stop. A few seconds between each pop.
Take the pan off the heat and tip your popcorn onto your large baking sheet that has been covered with baking parchment and allow it to cool.
Take your white chocolate and if using a bar break it up into small pieces and place it in a bowl, if using chips place them in a bowl and melt. Either in the microwave on a medium power for 10 seconds at a time, or over a small pan of boiling water or in a double boiler.
Pour the melted chocolate over the popcorn and mix it until all of the popped corn is fully coated. Spread the corn out to a single layer and allow the chocolate to cool back down and harden again. About 30 minutes should do it, or hasten it along by popping it in the fridge.
Once the chocolate is set sprinkle the cranberries in with the corn, give it another quick mix then enjoy. You can store this in an airtight container for up to 5 days. But is best enjoyed fresh.