Cut potatoes into bite-sized pieces, soak in water, and drain. Cut mentaiko to remove the roe and quarter the cheese slice.

Place potatoes in a pot, add enough water to cover them, and boil over medium heat for 10 minutes. Drain the water.

Mash the potatoes in a bowl until smooth.

Add potato starch and salt to the mashed potatoes and mix well. Let cool slightly.

Mix mentaiko roe and mayonnaise in a separate bowl.

Divide the potato mixture into 4 portions, flatten each on a piece of plastic wrap, add cheese and mentaiko mayo mixture, and wrap to form a ball.