01 - Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, ensuring there's an overhang for easy removal.
02 - In a mixing bowl, combine flour, dark brown sugar, ground ginger, cinnamon, cloves, baking powder, and salt. Incorporate the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Set aside.
03 - In a separate large mixing bowl, cream the softened butter and granulated sugar until the mixture is light and fluffy. Beat in the eggs one at a time, followed by the vanilla extract.
04 - In another bowl, whisk together flour, baking powder, and salt. Gradually add half of the dry ingredients to the wet butter mixture, mixing until just combined. Add the milk, then incorporate the remaining dry ingredients. Mix until the batter is smooth.
05 - Spread the cake batter evenly into the prepared baking pan. Sprinkle half of the prepared gingerbread crumble mixture over the cake layer.
06 - Scatter mini marshmallows, festive sprinkles, and mini chocolate chips over the top of the crumble for a decorative effect.
07 - Evenly distribute the remaining gingerbread crumble over the decorated cake layer.
08 - Bake for 33–37 minutes, or until the top is golden brown and a toothpick inserted into the center emerges clean.
09 - Allow the bars to cool completely in the pan. Use the parchment paper overhang to lift the entire block from the pan, then cut into individual bars before serving.