Line a baking sheet with greaseproof paper and put to one side for now.
In a stand mixer or mixing bowl, add the butter and sugar. Mix together until light, fluffy and smooth.
Add the flour and combine to get a smooth paste. It may look a little crumbly, but it will hold together. Add the cranberries.
Lightly flour a work surface and roll out your dough to approximately 1cm (1/2 an inch) thick.
Using a cutter, cut into 10-12 rounds and place on the baking sheet. You'll probably end up with one biscuit made up of the leftovers from the rest - this is my favourite as it's always the first to get eaten!
Put the biscuits in the fridge for 20-30 minutes to firm up. Preheat the oven to 350 ºF or 175 ºC.
Sprinkle some caster sugar on the top, and then pop in the oven for 15-20 minutes or until golden brown on the top.
When they're ready, remove the biscuits from the oven and let them cool on a wire rack.
While the shortbread biscuits are cooling, melt some white chocolate in a small bowl over a pan of hot water (or using a microwave).
Either using a spoon to drizzle, or a piping bag with small nozzle fitted, drizzle the melted white chocolate over the shortbread biscuits. Make yourself a cup of tea and enjoy!