Cover icing at all times to prevent hardening. To store several hours or overnight, place plastic wrap directly on surface of icing; refrigerate. Before using, beat with mixer until stiff.
To hang on tree, slip a piece of thin ribbon through house; tie into bow.
Don't have a pastry bag? Use a small resealable bag instead. Cut small piece off one of the bottom corners of bag; seal bag. When ready to assemble house, gently squeeze top of bag to pipe icing.