To make the side walls place one pop tart onto your cutting board. Place a second, on it's side next to it. Cut the first pop tart across the top, using the second pop tart as a guide (as shown in photo). Repeat with another pop tart.
You should now have two roof pieces (un-cut), 2 house-shaped pieces, and 2 wall pieces.
Combine powdered sugar and water to make a royal icing glue. Add water 1/2 teaspoon at a time until desired consistency is achieved (2 1/2 teaspoons works well for me). Spoon icing into a Ziploc bag and cut the tip off. Glue the 4 walls together with icing and hold in place for a minute or so.
Add the roof pieces and hold in place for a minute or so.
Run a line of icing down the center of the roof to add even more stability.
Let houses stand AT LEAST 30 minutes before decorating. If making these with kids, assemble the houses the day before you want to decorate them to allow the pop tarts to harden a bit.
Dip decorations into icing or pipe icing onto houses to decorate.
Note: the pot of gold is made from an Oreo (cut with a serrated knift to make a flat top for the pot), and gold sixlets candies.