Important - Bird's Custard Powder is in itself a gluten free product but the label states it is made in a factory where gluten is handled so depending on your sensitivity to gluten, this brand could be unacceptable to you. Certified Gluten Free custard powders are available by other manufacturers or you can make your own (Google will tell you how until I perfect a recipe!). Failing that, use 1 tbsp of certified gluten free cornflour and an extra teaspoon of vanilla extract. Note that the flavouring in Bird's custard is actually almond not vanilla!
Adapted from from a recipe by Juvela, the gluten free product manufacturer