Preheat oven to 350degrees F. Line your baking sheet with foil or parchment paper and grease it. Set aside.
In a medium bowl, whisk the flour, baking powder and salt. Set aside.
In a large bowl, whisk the butter and brown sugar until frothy (about 2 minutes). Add the egg, vanilla and molasses (if using). Whisk again.
Slowly add the dry ingredients to the wet and stir with a spatula until fully combined. Add the white chocolate chips and craisins and fold again until evenly distributed.
Scoop the batter into prepared baking pan. Press down until it is an even layer then bake for 20-24 minutes until lightly golden. It will appear to be slightly underdone, but these are soft cookie bars and they will finish cooking in the hot pan outside of the oven.
Cool completely before frosting or pop in the fridge for an hour and then you'll be ready to frost.