In a large bowl, whisk together the flour, baking powder, ginger, cinnamon, cloves or allspice, and salt. Set aside.

Using a stand mixer fitted with the paddle attachment, beat the butter and brown sugar on medium speed until fluffy and well blended. Beat in the eggs, molasses, and water until well combined.

Beat half of the flour mixture into the molasses mixture until well blended and smooth. Add in the remaining flour and continue to mix until well blended and a soft cohesive dough forms. Turn the dough out onto a slightly floured work surface and knead by hand 5 or 6 times until the dough is smooth and combined. If dough is too soft, add a little more flour.

Divide the dough in half, pat into disks, and wrap each half in plastic wrap. Refrigerate for at least two hours, preferably overnight.

Preheat oven to 350°F, with the oven rack in the middle. Have 2 to 3 flat cookie sheets ready.

Spread parchment paper on a large flat surface for rolling. Dust the paper lightly with flour. Working with one portion of the dough at a time, use a rolling pin to roll out the dough to an even thickness of ¼ inch.

Rub a little flour over the surface of the dough. Place the pattern pieces on the dough, as many pattern pieces as will fit on the dough. Use a small sharp knife to cut out the pattern pieces from the dough.

Bake in a 350°F oven until the edges are just beginning to darken, 11-15 minutes for the large pieces, 6 to 8 minutes for the small pieces. Remove the sheets to racks to cool, about 15 minutes.

While the pieces are still slightly warm, lay the pattern pieces over them and use a large straight chef's knife to trim off any parts of the pieces that have through cooking spread beyond the pattern.

Whisk the egg whites and 1 ⅓ cups of the powdered sugar together until smooth. Add the remaining 1 ⅓ cup of powdered sugar to the sugar egg mixture. Using an electric mixer, beat on high speed until the icing holds stiff peaks.

When you are ready to mortar or decorate, fill a pastry bag with the icing. Pipe a thick line of icing along a short end of one of the side pieces. Press the iced side piece against the edge of either the front or back pieces.

Let set for at least an hour before attempting to add the roof pieces. Once the royal icing has dried enough so that the base structure is solid, you can go to work on the roof.

Decorate your gingerbread house with piped royal icing and candies such as red hots, gum drops, candy canes, chocolate truffles, or whatever you like.