These are better than any store-bought, all amounts may be doubled for a 13x9-inch pan - if you don't have custard powder on hand then use instant vanilla pudding powder instead, you may have to adjust the amount according to the texture desired, start out with 2 tablespoons adding more to achieve desired texture, I have to say that these bars are better both in taste and appearence if made with the custard powder and you will easily find it in the baking section near the pudding mixes of any grocery store, what you do not use will keep well covered tightly in the fridge so I advise to purchase the custard powder! - and for easier slicing chill the bars just slightly then remove from fridge when just partially hard then run a sharp knife through the bars to slice into desired sizes then return to fridge to finish chilling, this will make slicing the bars easier when they harden - different flavored extracts and food colouring may be used to create different flavors, such as mint extract and a drop of green food colouring, also these freeze very well! :)