Evenly spread yogurt into a 9-inch square baking pan lined with plastic warp. Freeze 45 minutes.

Meanwhile, prepare Royal Icing: In a bowl, with mixer on low, combine confectioners' sugar, powdered egg whites, and water. Increase speed to high, and beat until stiff peaks form. Tint half with pink icing color. Place icings in plastic resealable bags. Snip off one small corner of each bag, and pipe valentine decorations onto 9 wafer cookies. Let dry.

Using a 2-1/2-inch round cookie cutter, cut out 9 circles from the yogurt. Place each circle onto an undecorated wafer cookie, and top with a decorated wafer. Place sanwiches in freezer until ready to serve.