Most sources recommend using royal frosting to glue your gingerbread house pieces together. This works, but it takes a long time to set up, which means you need to find ways to keep the house propped up while it dries.
We glue our houses together with boiling sugar. It's dangerous but very effective. I have no idea where we got this technique, but it's easily the most exciting/terrifying part of the whole process.
The technique is simple - pour 3 or 4 cups of sugar in a large cast iron skillet and heat it until it starts to boil, stirring occasionally, then lower the heat to the lowest setting or turn it off completely. If it starts too get too thick while you work, hit it with a bit more heat.
You have to have everything ready and you need two people. Wearing gloves helps in case you accidentally drip hot sugar on yourself, but it's best if you also have a big bowl of ice water next to your work station, just in case. Hot sugar causes terrible burns, so it pays to be safe even if you don't end up needing it (my sister and I both came out unscathed this year).
One person should dip the edges of a piece in the sugar and the other person will hold the other pieces ready. The sugar cools quickly, so you have to work fast. Press the pieces together and hold it for 5 seconds or so while it sets up.
Here's how we did it, specifically.
- Kick all pets and children out of the house. Or at least out of the kitchen.
- One person holds the front and back of the house up. The other person dips the edges of a house side wall in the sugar and then carefully positions it between the front and back pieces. Repeat with the second wall. Set the base of the house aside for at least 5 minutes (this gives it a chance to really set up, which will make it sturdier for the next step). If you work assembly line style, you can get all the house bases set up and then go back down the line and attach the roofs.
- The roof is the tricky part. One person should hold both roof pieces while the other person picks up the entire base of the house and dips the top edges in the hot glue (this is where you are most likely to get burned, so be careful). Set the base down and press the roof pieces in place. Let it cool for 5 - 10 seconds and then tip the house over again and dip the roofline in the sugar (this just ensures that the roof is nice and secure).
- Have a base ready. We just use a rectangle of cardboard covered with aluminum foil. Dip the bottom of the house in the sugar and position it on the base. This keeps your house from shifting around, which is critical if you're going to transport it. Add the door, if desired, by dipping one edge in glue and sticking it on the house.
Voila! Finished houses that will not come apart, no matter what you do and are completely edible.