Cut the potatoes into bite-sized pieces, soak in water for 5 minutes, and drain.

Make a slit in the cod roe and extract the contents. Cut the mozzarella cheese into 1cm cubes.

Place the potatoes in a pot, add enough water to cover them, and boil over medium heat until a skewer easily pierces through. Drain the water and heat again to evaporate excess moisture.

Transfer the potatoes to a bowl and mash them.