Make the gingerbread brownies

1. Prepare the pan and oven.
   Set the oven to 350°F. Line a 9×9-inch baking pan with parchment paper, leaving enough overhang to lift the brownies out later. Set the pan aside.
2. Mix the butter and sugar.
   In a large mixing bowl, stir the melted butter and brown sugar together until the mixture looks smooth and evenly combined.
3. Add the eggs, molasses, and vanilla.
   Stir in the eggs, molasses, and vanilla extract. Mix until the batter looks glossy and fully blended.
4. Combine the dry ingredients.
   In a separate bowl, whisk together the flour, ground ginger, cinnamon, baking powder, and salt.
5. Finish the batter.
   Add the dry mixture to the wet ingredients a little at a time, stirring just until no streaks of flour remain. Do not overmix.
6. Bake.
   Spread the batter evenly into the prepared pan. Bake for 28 to 33 minutes, or until the outer edges look set and the center no longer moves when you gently shake the pan.
7. Cool completely.
   Remove the brownies from the oven and let them cool fully in the pan before adding the frosting.

Make the gingerbread ermine frosting

8. Cook the flour and milk mixture.
   While the brownies cool, place the milk and flour in a medium saucepan over medium heat. Whisk constantly for 3 to 5 minutes until the mixture thickens, all lumps disappear, and the texture resembles very thick pudding. It should coat the back of a spoon.
9. Cool the base mixture.
   Take the pan off the heat and let the mixture return to room temperature. Lay plastic wrap directly on the surface to keep a skin from forming while it cools.
10. Cream the butter and sugar.
    In the bowl of a stand mixer fitted with the paddle attachment, beat the room-temperature butter and brown sugar on medium speed for 2 to 3 minutes, until the mixture turns pale and fluffy. Scrape down the bowl with a rubber spatula as needed.
11. Add the cooked mixture and spice blend.
    Once the milk mixture has cooled completely, add it to the mixer bowl along with the gingerbread spice mix. Beat on medium-high speed for 2 to 3 minutes, until the frosting becomes airy and smooth. Stop to scrape the bowl whenever necessary so everything mixes evenly.
12. Whip until silky.
    Swap to the whisk attachment. Add the vanilla extract and mix on high speed for 7 to 8 minutes, or until the frosting looks creamy, fluffy, and very smooth.
13. Assemble and serve.
    Spread the frosting over the cooled brownies in an even layer. Cut into squares and serve.