Nononononononononono. Don't do the microwave method. The stovetop method is easy peasy. Two tbsp custard powder, 1.5 tbsp sugar, 2 tbsp milk taken from one pint -> mix to smooth paste. Heat rest of milk until it is steaming and just starting to form bubbles around the outside. Add hot milk to custard a little at a time, then return all to pan and bring to boil while stirring until it thickens.
I can't make custard from scratch, I specialise in vanilla scrambled eggs when I try, but like the Birds custard made from the old-fashioned powder better than the pre-made stuff. I find the sachet stuff you just add water to much harder than the old powder you add sugar and milk to.