Prep. Preheat oven to 350 °F and butter the bottom and sides of an 8-inch square pan. Optionally, line the bottom of the pan with parchment for easiest removal of brownies after baking.
Make gingerbread swirl. Beat 4 oz cream cheese until smooth, 1 minute. Add egg, 2 tbsp sugar, 2 tsp molasses, 2 tbsp flour, pinch of salt, and spices (¼ tsp ginger, ½ tsp cinnamon, pinch cloves). Beat ingredients together until completely smooth. Set aside.
Make brownie batter. Whisk 4 oz melted butter and 1 ½ cups brown sugar in a large bowl. Add 1 tbsp molasses, 2 eggs, 1 tsp salt, and 2 tsp vanilla. Whisk vigorously until mixture is silky smooth, thick, and ribbony, 1-2 minutes.
Whisk together 1 cup cocoa powder and ½ cup flour. Gently fold into butter mixture, mixing just until combined.
Swirl. Spread brownie batter in prepared pan. Dollop gingerbread mixture over top. Use a knife to swirl the batters together lightly, creating a marbled look.
Bake. Bake brownies until sides are set and middle looks just slightly underdone and shiny, about 25-30 minutes. Cool brownies completely before slicing.