Makes 24 cookies
1/2 teaspoon baking powder
Preheat oven to 375 degrees Fahrenheit. Line 2 baking sheets with parchment paper or Silpat baking mats.
In a medium bowl, whisk together flour, baking powder, baking soda and salt. Set aside. In the bowl of an electric mixer, cream together the butter and both sugars until light and fluffy. Add the egg and vanilla extract until well mixed. Scrap the sides of the bowl with a rubber spatula. Then, with the mixer on low, gradually add the flour mixture until just combined. Using the rubber spatula, stir in the oats, white chocolate chips and dried cranberries. The dough will be very thick and somewhat crumbly.
Roll the dough into 2"-ish balls and place on the baking sheets. Flatten the tops sightly with your fingers. Bake both cookie sheets for 10-12 minutes, rotating and reversing the pans halfway through baking, until the tops are light golden brown. Cool on the pan for a minute and remove to a wire rack to cool further.
Store in an airtight container at room temperature.