Preheat the oven to 350°F (177°C) and prepare a 9x9-inch baking dish.

In a large mixing bowl, whisk together melted unsalted butter and light brown sugar until smooth. Add eggs, molasses, and vanilla extract, stirring until glossy.

In another bowl, whisk together flour, ground ginger, cinnamon, baking powder, and kosher salt until combined.

Gradually fold dry ingredients into wet ingredients until just combined, without overmixing.

Spread brownie batter in the prepared baking dish and bake for 30-35 minutes, until edges are set and a toothpick comes out with a few moist crumbs.

Allow brownies to cool for 10 minutes in the pan, then transfer to a wire rack to cool completely. Dust with confectioners' sugar and slice into squares before serving.