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! :)
02For microwave method; melt the butter with sugar in microwave until the butter is completely melted, removing one time to stir (you do not have to cook until very hot) mix in cocoa powder until well combined, then vigorously whisk in eggs until combined, then stir in remaining ingredients (the mixture will be thick so I always mix with my hands).
03Press firmly into prepared ungreased 8 x 8-inch square pan.
04For the middle layer: cream butter, half and half, custard powder and icing sugar; beat until light and creamy.
05Spread over the bottom layer; refrigerate for 10-15 minutes.
06For the topping: In the microwave, or on top of the stove, on low heat, melt the chocolate squares with the 4 Tbsp butter; stirring to combine adding in the whipping cream for a more creamier texture if desired.
07Pour evenly over the middle creamy layer (smooth out with a spoon to even out if necessary).