For the cookies: In a medium bowl, combine the flour, ginger, cinnamon, nutmeg, baking soda, cloves and salt.
In a big bowl, beat the butter and brown sugar together with a wooden spoon or a hand mixer. Mix in the molasses and egg until smooth, then add the flour mixture and mix until well combined. Wrap the dough in plastic wrap and refrigerate for 1 to 2 hours.
On a floured surface, roll out the dough to about 1/8-inch thickness. Freeze it flat on a baking sheet for 20 to 30 minutes.
Preheat the oven to 350 degrees F and line 2 baking sheets with parchment paper. Lightly spray the paper with cooking spray.
Use your preferred cookie cutters to stamp out shapes (or use a paring knife and architect the gingerbread home of your dreams), then transfer the shapes to the prepared baking sheets. Bake until the dough no longer looks shiny, 18 to 20 minutes. Let cool on the sheets for 10 minutes, then transfer the cookies to a wire rack to cool completely.
For the royal icing: Using a stand mixer and the whisk attachment, whip most of the powdered sugar with the egg whites and most of the lemon juice. Whip until the icing holds its shape and is bright white (not translucent), 5 to 8 minutes. If it is too soft, add more powdered sugar. If it is too stiff, add a bit more lemon juice, drop by drop. If you are using color, add a few drops of it at this point and keep whipping until you have a shade you want. Pipe the royal icing onto the cooled cookies to decorate.
To store royal icing: The ideal way is to scrape it out of the bowl and into a plastic, disposable piping bag, then leave it at room temperature. Don't cut the bag until you're ready to use the royal icing and don't overfill the bag--you want enough room to tie the back of the bag off to keep the icing airtight. If any air comes into contact with the icing, it gets hard and that part of the icing is useless. Never attempt to mix hard bits back into the royal icing--you'll ruin the whole batch. The other accepted method of storing the icing is to scrape it into a plastic or ceramic bowl, and cover it with a wet paper towel. This method works, but it wastes both paper towels and royal icing. It's also just annoying. When you're piping small designs, you want to use very small parchment piping bags. It's easy to stick the nose of a large piping bag into a small one and extract exactly how much you need. When the icing is in a bowl, you have to use a spoon to get it out. The spoon is difficult to get into a piping bag, and you keep using spoons and wasting royal icing.
You can also make the royal icing with meringue powder instead of egg whites. Use 4 cups powdered sugar, 3 tablespoons meringue powder and 5 to 7 tablespoons water. Using a stand mixer and the whisk attachment, whip most of the powdered sugar with the meringue powder and most of the water. Whip until the icing holds its shape and is bright white (not translucent), 5 to 8 minutes. If it is too soft, add more powdered sugar. If it is too stiff, add a bit more water, drop by drop. You can also substitute royal icing powder. CK Products brand is my favorite.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.