Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, baking soda, cinnamon and ginger. In a large bowl, mix together butter, sugar, and molasses until fluffy. Add in the egg and vanilla extract and mix until smooth.
Add in the flour mixture and mix until it is fully combined. Fold in the white chocolate chips. Evenly press the cookie dough into the baking dish and bake for 20-25 minutes.