- 1 1/4- to 3/8-inch-diameter plain round pastry tip
Place 14-inch round cardboard base on work surface. Spoon some icing into pastry bag fitted with 1/4- to 3/8-inch-diameter tip; cover icing in bowl tightly to prevent drying. Pipe small dab of icing in center of round. Place one 7X10-inch cardboard foundation rectangle on icing; press to adhere. Pipe small mound of icing in center of rectangle. Place second 7X10-inch rectangle over; press to adhere. Repeat with more icing and remaing two 7X10-inch rectangles, forming foundation for house in center of round cardboard base.
Pipe thick line of icing on bottom edge of 1 side wall. Stand wall on cardboard foundation, icing side down, 1 inch in from and parallel to 1 long side and 2 inching in from 1 short side; hold 5 minutes. Pipe thick line of icing onto front edge of wall. Press back edge of front wall (with door cutout) into icing on front edge of side wall. Hold pieces together 5 minutes. Pipe thick line of icing onto bottom edge and up front edge of second side wall. Press icing on front edge into back edge of front wall. Hold for 5 minutes. Pipe line of icing up back edge of each side wall. Press edges of back wall into icing, forming back of house. Hold 5 minutes to set. Pipe lines of icing inside house at 4 intersections of walls, along base and on outside at all vertical joints to reinforce. Pipe thick line of icing along 1 long edge of front-door cookie. Attach cookie to left side of door opening in front wall, creating an opened front door. Pipe any icing left in pastry bag back into bowl of icing. Cover tightly; store at room temperature to use for decorating later. Let house stand until icing is completely dry and very hard, about 12 hours.