It takes less than 10 minutes to make.
250-300 grams sweet potato (washed, dried and cut into bite size pieces)
4 Tablespoons sugar (wasanbon if you have it, if not, regular sugar or try brown sugar)
1 teaspoon soy sauce
1 teaspoon vinegar (this helps the sugar from hardening when it cools down)
1/2 teaspoon salt
4 Tablespoons salad oil
a bit of water
toasted black sesame seeds
Put the sweet potatoes, sugar, soy sauce, vinegar, salt, salad oil and water in a fry pan and put over medium high heat. Place a lid over it and after two minutes stir the mixture. After another two minutes stir again, and start to watch (and smell) that the sugar does not burn. After six minutes, check to see if the sweet potatoes are cooked, and then move to a plate to serve. Sprinkle with black sesame seeds and allow for the sugar to cool a bit before serving.
You too may become addicted to these "daigaku imo" sweet potatoes.