Preheat your oven to 350°F (175°C) and line a 9x13-inch baking pan with parchment paper.
In a large mixing bowl, combine the flour, baking soda, ginger, cinnamon, nutmeg, and salt; whisk until blended.
Melt the butter and whisk in the brown sugar, granulated sugar, molasses, egg, and vanilla extract until smooth.
Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Fold in optional white chocolate chips if desired.
Spread the dough into the prepared baking pan and bake for about 25 minutes or until a toothpick comes out clean.
Let cool in the pan for at least one hour before lifting out and cutting into squares.