Mix the dry ingredients: Whisk together the flour, baking soda, salt, ginger, cinnamon, cloves, and nutmeg in a medium bowl.
Cream the butter and sugar: In a large bowl, beat the softened butter and brown sugar until light and creamy.
Add the wet ingredients: Beat in the egg and vanilla. Add the molasses and mix until smooth.
Make the dough: Gradually add the dry ingredients and mix just until a soft dough forms. Divide the dough into two portions, flatten into disks, wrap, and refrigerate for at least 1 hour.
Preheat the oven: Heat the oven to 350°F (175°C). Line baking sheets with parchment paper.
Roll the dough: Lightly flour your work surface and rolling pin. Roll the chilled dough to about 1/4-inch thickness.
Cut the stars: Use graduated star-shaped cookie cutters to cut several sizes of stars. You’ll need multiple stars in each size for the stacked tree.
Bake: Carefully transfer the cookies to the prepared baking sheets. Bake for 8–12 minutes, depending on their size, until the edges are set. Let them cool on the baking sheet for 5 minutes, then transfer to a wire rack.
Make the icing: Whisk the powdered sugar and meringue powder together. Gradually add the water and vanilla until you have a thick, pipeable royal icing. Add a few drops of water if it is too thick, or more powdered sugar if it is too thin.
Build the tree: Place the largest star on a serving plate. Pipe a small amount of royal icing in the center and place another star on top. Continue stacking from largest to smallest, rotating each layer slightly.
Decorate: Pipe thin lines of royal icing around the edges to create a snowy effect. Add sprinkles, edible pearls, or small candies while the icing is still wet.
Finish: Lightly dust the finished Gingerbread Christmas Tree with powdered sugar. Allow the icing to set before serving.