Preheat the oven to 350°F. Line a 9×13-inch baking dish with parchment paper, including up the sides. Set aside.
In a large microwave-safe bowl, add the butter and the white chocolate chips. Melt in 20-second intervals, stirring in between each time, until the mixture is creamy with no lumps (about 1-2 minutes total). Allow to slightly cool.
To the melted white chocolate mixture, add brown sugar. Stir to combine.
Add the eggs and the egg yolk, one at a time, stirring well after each addition.
Stir in the vanilla extract and the orange zest. Set aside.
In a separate bowl, whisk together the flour, cornstarch, baking powder, salt, and ginger.
Add the dry ingredients to the wet ingredients and stir until completely combined. Fold in the dried cranberries.
Spread the batter evenly into the prepared pan. Bake for 25-30 minutes, or until the edges just begin to turn golden brown.
Allow to cool completely before topping with frosting.