Preheat the oven to 400°F (200°C)
Wash the Japanese sweet potatoes thoroughly
Pat them dry
Pierce each potato several times with a fork
Place the potatoes on a baking sheet lined with parchment paper or foil
Bake for 45 to 60 minutes, depending on size
Turn them once halfway through baking
Check for doneness by inserting a knife or skewer; it should slide in easily
Remove from the oven
Let them cool for a few minutes before serving