Roughly chop white chocolate and cranberries (each cranberry should be cut into 2-3 pieces). Toss the cranberries with 1 tablespoon of flour until coated on all sides.
Preheat the oven to 375°F / 190°C / Gas Mark 5, no fan (if you have a convection oven reduce the temperature by about 20° or follow the manufacturer's instructions).
Add the softened butter and both types of sugar into the mixing bowl. Mix over medium-low speed for about 3-5 minutes, until light, fluffy, and well-combined (you can use a hand mixer or a stand mixer, if using a stand mixer use a paddle-shaped attachment).
Add the egg and vanilla extract, mix over medium-low speed for another 3-5 minutes, until well-combined. Scrape the sides of the bowl from time to time with a spatula.
Stir the flour with baking soda and salt. Add the flour mixture to the mixing bowl. Mix over low speed until half combined (you should still see flour here and there and the dough will be rather clumpy).
Add the chopped chocolate and cranberries to the bowl. Mix until they are evenly distributed, but the dough should be clumpy.
Scoop the dough with a 3-tablespoons-ice cream scoop or just with your hands/spoon. Gather the dough clumps with your hands then roll it into balls (every ball should weigh 40g/1.4oz). Don’t flatten the balls. Place on a baking sheet lined with parchment paper about 2 inches (5 cm) apart.
Bake for about 14 minutes. Bake the cookies in batches. The baking time may slightly vary depending on the oven. The cookies should have golden edges but will be completely soft.
Take the baking tray out of the oven and let the cookies cool on the baking sheet (they will continue to set up from the residual heat on the pan after they come out of the oven).
Enjoy!