Peel the sweet potato and slice it into 1cm thick pieces.
Boil the sliced sweet potatoes in boiling water for 5 minutes.
Drain the boiled sweet potatoes using a sieve and let them cool.
Place the sweet potatoes on a slice of bread and sprinkle with honey or sugar.
Spread a thin layer of mayonnaise, then cover with another slice of bread.
Melt butter in a pan and grill the sandwich on both sides until golden brown.
Cut into desired sizes and serve on a plate.