Special equipment: a 9-cup gingerbread house cake mold and 2 pastry bags
For the cake: Preheat the oven to 350 degrees F and generously spray a 9-cup gingerbread house cake mold with nonstick baking spray.
Whisk the flour, gingerbread spice and salt in a medium bowl. Set aside. Whisk the molasses, oil and granulated sugar in a large bowl. Combine 1 cup boiling water with the baking soda in a heat-proof measuring cup and stir to dissolve. Whisk the water mixture into the molasses mixture until well combined. Whisk in the flour mixture and then the eggs until combined.
Pour the batter into the prepared cake mold and bake until the edges are set and a toothpick inserted in the center comes out clean with a few wet crumbs, 50 to 55 minutes. Cool for 10 minutes in the pan before unmolding onto a cooling rack to cool completely.
For the icing: Combine the confectioners’ sugar and meringue powder in the bowl of an electric mixer fitted with the whisk attachment. Add 5 tablespoons water and beat on medium-high speed until the icing forms thick and glossy peaks, about 2 minutes, adding up to 1 tablespoon more water, if needed.
Transfer 1/2 cup of the icing to a small bowl, add food coloring for desired shade of green and stir to combine. Transfer the green icing to a piping bag and snip off the tip. Transfer the remaining icing to a second piping bag and snip off the tip.
For the decorations: Transfer the cake to a baking sheet or decorative tray. Use the green icing to pipe trees and shrubbery on the sides of the house. Use the white icing to pipe windows and outline the roof and eaves. Sprinkle with the shredded coconut for snow. Decorate the house and grounds with candies such as gumdrops, candy canes, shaved chocolate, cinnamon sticks, white chocolate chips, cinnamon candies and red sanding sugar.