In a large bowl, cream butter and sugar until light and fluffy. Beat in the egg yolks, molasses and water. Combine the flour, baking soda, cinnamon and baking powder; gradually add to creamed mixture and mix well. Cover and refrigerate for 2 hours or until easy to handle., On a lightly floured surface, roll out dough to 1/8-in. thickness. Cut with a floured 2-1/2-in. round cookie cutter. Place 1 in. apart on ungreased baking sheets. Bake at 375° for 8-10 minutes or until edges are firm. Remove to wire racks to cool. , For frosting, combine the sugar, egg whites and water in a small heavy saucepan over low heat. With a hand mixer, beat on low speed for 1 minute. Continue beating on low over low heat until frosting reaches 160°, about 8-10 minutes. Pour into the bowl of a heavy-duty stand mixer; add confectioners' sugar. Beat on high until frosting forms stiff peaks, about 7 minutes. Frost cookies. Let stand until dry.