Preheat oven to 350°F (175°C). Grease a 9"x 13"x 2" baking pan.
Whisk together the flour, baking powder, and salt. Set aside.
Using an electric mixer on medium speed, beat the butter and sugar until thoroughly combined. Add the eggs, one at a time, mixing well after each addition. Mix in the vanilla.
Reduce mixer speed to low and gradually add the flour mixture, mixing just until combined.
Stir in the cranberries and white chocolate.
Spread the dough evenly in the prepared pan.
Bake 35-40 minutes, or until the bars are golden brown and a pick inserted into the center comes out clean.
Cool in the pan on a wire rack.
To make the glaze:
Combine the confectioners' sugar and 1 tablespoon of milk, stirring until smooth. Add more milk, a small amount at a time, until the glaze is thick but pourable.
Drizzle the glaze over the cooled bars. Cut into bars and serve.