FROSTED HOLIDAY SUGAR COOKIES

Steps:

• In a large bowl, whisk together flour, baking soda, cream of tartar and salt.
• In the bowl of an electric mixer, cream the butter and sugar until fluffy. Beat in vanilla, then beat in egg.
• Add flour mixture and beat until just combined. Divide the dough in half, pat into flat rectangles, wrap in plastic and chill for at least 2 hours.
• Divide each dough parcel in half, and roll out to 1/8-inch thickness between two sheets of parchment paper or plastic wrap. Repeat with remaining dough. Chill until firm, about 20 minutes.
• Heat the oven to 350 degrees. Line four cookie sheets with parchment paper, sprinkling with a little flour if the dough seems sticky. Cut out shapes from the rolled and chilled dough and place on prepared sheets 1-inch apart. Bake until golden around the edges, 8 to 13 minutes. Let cool.
• Meanwhile, prepare the royal icing: in the bowl of an electric mixer, combine the sugar, egg whites, cream of tartar, and salt. Whisk until stiff and glossy.
• To tint the frosting, divide into small bowls. Cover the ones you aren't using with plastic wrap; the frosting dries out very quickly. Use a rubber spatula to stir in desired food coloring. Though not necessary, it makes life easier if you make two versions of each color - one that is thick to pipe the outline on the cookie, and one that is thinned out slightly with a little water to flood the outline. Transfer frosting to piping bags fitted with very small round tips (sizes 1 to 2 work best).
• Pipe frosting onto cooled cookies and let set, at least 2 hours. Or use a pastry of paint brush to decorate cookies with the frosting.