Use butter at room temperature, as it mixes better with all the other ingredients. If you have forgotten to take it out of the fridge, leave it out at room temperature for about an hour before making up the dough.
Always use block butter when making these cookies. Spreadable butter will not firm up enough and will result in baked cookies that are likely to spread more and not hold their shape.
When adding in the dry ingredients, mix until combined before squeezing the dough together into a disc. Over beating the dough can result in overworking the gluten, creating tough cookies and not soft, melt-in-your-mouth ones.
Chilling the dough is important, for two reasons. It allows the gluten to relax, making sure the cookies are not tough when baked. And it also allows the butter to chill again, ensuring the cookies hold their shape during baking.
Keep an eye on the cookies as they bake. They can catch on the edges very easily, so if you want the cookies to remain pale and not golden, it could be the difference in a minute of baking time!
When making the royal icing, add in the water just a few drops at a time. A little goes a very long way when it comes to making icing! You are looking for a fairly thick texture that still flows back together and blends smooth after about 15 seconds.
Always use gel colours when colouring royal icing. Gel colours are more concentrated so you will require less to achieve the colour you want. They also contain less water, so will not affect the consistency of the icing.
You can use a nozzle if you prefer rather than cutting the end of the piping bag. If using a nozzle I would recommend not using a larger tip than no. 3.
Pipe the outline of the cookie shape before filling it in with icing. Once filled in, gently shake the cookie to spread the icing out and level it. Use a toothpick or a pin to remove any air bubbles and smooth the icing over before leaving the base layer to set.
The way I have decorated the cookies here is by allowing the main base colour to dry completely before adding details on top. You can add the details to the wet base colour of course. However, this would result in the icing all being one layer, not textured.
Leave the icing to dry completely for a few hours before storing in an airtight container.