Microwave pudding sediments
Unlike with stovetop recipes, you need not heat the major part of your milk first and then add the starch slurry, you can mix everything while cold. As with all similar microwave recipes, using a wide bowl (preferably with straight sides) is best suited for the job. Use short microwave intervals at medium power, give the mix a quick stir with a whisk every minute or so. You want to heat the milk as evenly as possible while keeping the starch more or less suspended. "Hot spots" will create the dreaded lumps, similar to not stirring well when cooking on the stove.

And when you reach a certain temperature threshold, the "magic" starts: gelatinization happens everywhere at roughly the same time and your whole mix thickens almost instantly. (Unlike in a pot, where it starts at the bottom.) Simmer half a minute longer or so, give it a final stir and your pudding is done.