In a saucepan, combine the butter, brown sugar and molasses. Cook over medium heat until butter melts and sugar dissolves, stirring constantly.
Pour into a mixing bowl. Add vanilla. Let cool for 5 minutes, then add the egg. Beat well. Stir the dry ingredients together, then add to the egg mixture. Mix well. Divide in half. Cover both halves, and chill 2 hours or overnight.
Roll to 1/4-inch thick on floured surface. Cut out with house- shaped cutter, and place on ungreased cookie sheet one inch apart. Bake at 350 degrees for 8 to 10 minutes.
Cool completely. Meanwhile beat egg whites on high until soft peaks form, beat in powdered sugar and lemon juice until stiff. Use food color to color icing. Pipe house details on the cookies with thin frosting tip.