Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper so that it hangs over the two longer sides.
In the bowl of a stand mixer fitted with a paddle attachment, cream together the butter, sugar and brown sugar until light and fluffy, about 2 minutes. 
Add the eggs one at a time, beating between each addition, then beat in the vanilla extract and orange zest.
Add the flour, baking powder and 1/2 teaspoon kosher salt and beat just until combined.
Stir in the white chocolate chips and dried cranberries then transfer the dough into the prepared baking pan, pressing it into an even layer.
Bake the bars until they are fully set and golden brown, about 25 minutes. Remove the bars from the oven and set them aside to cool completely while you make the topping.