I think, Aveline that Fleur is saying that it will have already been cooked prior to you receiving it, so that it’s second steaming is when you take it out if it’s box. This second steaming (reheating) can either be done conventionally, by steaming in a pan of hot water, heated in a slow cooker or microwaved. As you are wondering if this stage can be done a portion at a time in the microwave, then yes, I think this is possible, as others say - just do it in short bursts, and keep checking. The remaining pud should keep well in the fridge if well wrapped up, or, as Fleur says, freeze these portions, then defrost & reheat as and when you want some. Enjoy ?