my favourite gingerbread

Name: my favourite gingerbread
Cuisine: European, British
Ingredients: 4-1/2 cups all-purpose flour; 1 tablespoon plus 2 teaspoons ground ginger; 1 tablespoon unsweetened cocoa powder; 2 teaspoons cinnamon; 1 teaspoon ground cloves; 1/4 teaspoon freshly grated nutmeg; 1 teaspoon baking soda; 1 teaspoon salt; 3/4 cup unsalted butter, softened; 3/4 cup firmly packed light brown sugar; 1 large egg, at room temperature, lightly beaten; 1 cup unsulphured molasses; 2 egg whites (or 1-1/2 tablespoons powdered egg white and 1/4 cup warm water); pinch cream of tartar (optional); 2 cups confectioner's sugar, sifted; food colouring (optional)