Preheat oven to 350°F. Line a 13x9-inch baking dish with parchment paper, leaving overhang on the sides.
In a medium bowl, whisk together flour, ginger, cinnamon, baking soda, salt, nutmeg, and cloves.
In a large bowl, whisk together the melted butter and brown sugar until smooth and well combined.
Beat in molasses, egg, and vanilla until incorporated.
Gradually mix in the dry ingredients, scraping down the sides as needed, until dough forms.
Press dough evenly into the prepared pan.
Bake 20–22 minutes, or until a toothpick inserted in the center comes out clean.
Cool completely in the pan on a wire rack before frosting.