1. Preheat the oven to 375 degrees F. Line two baking sheets with parchment paper or a silicone baking mat; set aside.
2. In a medium bowl whisk together the flour, baking powder, baking soda and salt; set aside.
3. In the bowl of a stand mixer, cream the butter and both sugars together until light and fluffy, about 3 minutes. Add the egg and the vanilla extract and mix until well combined. Reduce the mixer speed to low and gradually add the flour mixture, mixing until just incorporated. Using a rubber spatula, stir in the oats, the white chocolate chips and the dried cranberries.
4. Roll dough into balls - about 2 tablespoons of dough per cookie - and place on the prepared baking sheets. Flatten the tops slightly with your fingers. Bake until cookies turn slightly golden about 10 minutes. Remove from the oven and let cool on the baking sheet for 2 minutes. Transfer to a wire rack until completely cool. Store in an airtight container at room temperature.