Cut the cabbage into 1cm cubes, sprinkle with salt, massage, and squeeze out excess water. Remove the cod roe from its casing using a spoon.

Cut the potatoes into bite-sized pieces, place them in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 7 minutes.

Remove the plastic wrap, add butter and salt and pepper, and mash the potatoes with a fork until smooth.