Preheat the oven to 350°F and line a baking sheet with parchment paper.
In a small bowl, whisk together the oats, flour, baking powder, cinnamon, and salt; set aside.
In the bowl of a stand mixer or using a handheld mixer, beat the sugar and butter on medium speed until creamed, 1 to 2 minutes. Add the egg, followed by the vanilla extract and beat until combined, 1 more minute.
With the mixer on low speed, slowly add in the dry ingredients and mix until just combined, without over mixing. Fold in the cranberries and white chocolate chips.
Divide the dough into 1 ½ tablespoon-sized balls using a spring-loaded scoop and press down slightly to flatten. Bake for 12-14 minutes or until cookie edges have set but the center still looks soft. Cool on the baking sheet for 5 minutes, then transfer to wire racks to cool completely.
Notes
Storage: Store in an airtight container for up to a week at room temperature.Freeze: Freeze solid on a baking sheet before transferring to a container or bag. They will keep well for up to 2 months and can be thawed at room temperature.Tip: Don't over mix the cookie batter when you add the flour so that the gluten doesn't over develop.Tip: Cool the cookies fully on a cooling rack before storing or serving.