In a medium bowl, whisk flour, baking soda, ginger, cinnamon, cloves and salt.
In a large bowl, beat butter and sugar until smooth. Beat in egg, then molasses. Stir flour mixture into butter mixture. Divide dough in half, wrap and chill for 2 hours.
Heat oven to 350°. On a well-floured surface, roll half of dough to 1/8-inch thickness. Cut into shapes with assortedsize gingerbread cookie cutters; transfer to ungreased baking sheets. Re-roll scraps and cut. Repeat with rest of dough.
Bake at 350° for 13 minutes. Transfer cookies to racks to cool. Decorate with Royal Icing, if using.
In a bowl, beat confectioners' sugar, powdered egg whites and 3 tbsp water until thick and shiny, about 5 minutes. Transfer to a pastry bag with a writing tip. Outline cookies and pipe on dots of frosting; add M&M's minis as buttons. Let dry.
