Peel your sweet potato. In my tests, 1kg sweet potato with skin on yields approximately 950g (2lbs) peeled sweet potato.
Cut the sweet potato into small-ish (roughly 1cm x 1cm or 1/2 inch x 1/2 inch) cubes and place into a large microwave safe bowl.
Microwave the sweet potato for 5 minutes.
After 5 minutes, thoroughly stir the sweet potato moving the pieces on top to the bottom. This ensures no sweet potato cubes get leathery skin that will make our puree chunky.
Return the bowl to the microwave and allow to sit in the steam for 5 minutes.
Repeat the process of cooking for 5 minutes, stirring and steaming. You may need to do this twice more, for a total of 15 minutes cooking time and 10 minutes steaming time, pending the amount of sweet potato you are cooking.
Once the sweet potato is soft, use a food processor to blend it into a smooth puree. If you are using a blender without a steam valve (like a NutriBullet) you will need to wait until the sweet potato has cooled.
Transfer the sweet potato puree to an airtight container and store in the fridge until you need to use it. You should have approximately 700-750g (1.54lbs - 1.65lbs). It keeps well in the fridge for a few days but can also be frozen and defrosted.