Tip the gingerbread house on its side, then using a tip 3 (or any small round tip), pipe the outlines for the window trim. Let the outline dry for 30 minutes to an hour.
Once the window trim outline is dry, use white icing to outline and fill in the shape of the frosted area. Work one windowpane at a time.
Use a small damp Decorator Brush to create texture by brushing the icing into the corners of the windowpane.
Sprinkle a small amount of White Sparkling Sugar on the icing, pressing the sugar to the icing very lightly if needed.
Notes
Let the window trim outline dry thoroughly before piping the snow and adding the sugar, or the sugar will stick to the window trim.