Royal icing is a little bit tricky because everyone has their own method. Some people like to outline with a thicker consistency and then fill with a runnier one, while others (like myself) like to use a single consistency for both steps. This recipe for royal icing is a basic one that can then be tweaked to make the consistency that you desire. My sugar cookie recipe can be found here. 

Ingredients:
2 eggs, whites only
3 cups powdered sugar
1 teaspoon vanilla
1 teaspoon lemon juice
Food colouring (optional) 

Directions:
Beat the egg whites and lemon juice until frothy, approximately 3 minutes. Add the vanilla and beat another 30 seconds. 

Add the sugar and beat on low for 8 minutes. This step is very important, in order for royal icing to set up and have a hard finish it needs to be properly beat at this stage. Your icing will be very thick. 

Add in the food colouring if you would like to colour the royal icing. Gel food colouring works the best here because it will not dilute the icing.

The next step is to add water, one tablespoon at a time until you get the consistency you desire and depending on your project. If you are piping a border or writing you will want to keep the icing very thick. For all my basic sugar cookie decorating needs I use a 10 second icing. 

10 second icing is when you run a spoon or knife through your icing and it takes 10 seconds for it to fill in and become smooth again. I use the 10 second rule because I outline and flood with the same consistency of icing and I find that the 10 second icing gives me a good balance between being able to pipe without the icing running off the edges and filling without too much effort. 

I like to use a Wilton #2 tip for my outlining and flooding because it gives me enough control to pipe the details and allows me to flood fairly easily as well. If you use different consistency icings you can use a larger tip for your flooding purposes. Regardless of the consistency of icing you use make sure you outline first and then fill. Allow the cookies to sit for 24 hours or overnight to let the icing set and harden.

If you are going layer your icing make sure you wait at least 4 hours in order for the bottom layer of frosting to dry sufficiently, like the way I have below with the elephant ears and eyes.

Another technique is the wet on wet technique, which allows you to have multiple colours on the cookie but to harden with a smooth finish rather than a layered finish. 

The way to do this is to apply the other colours while the base colour is still wet, as I've done below with the onesie. As soon as I finished flooding the cookie with the blue icing, I made the green polka dots. When the icing dried and hardened, it was a smooth finish. 

Once your icing has dried for 24 hours (or overnight) the icing should be hard and stackable. These cookies store very well in an airtight container for weeks. Or you can freeze them, fully decorated, for up to 3 months.

For my perfect cut-out sugar cookie recipe click here.