Peel the potatoes and cut them into smaller and uniform sizes.

Boil them in unsalted water for about 20 minutes - until they are tender.

Drain them, but keep 1-2 dl of the cooking water.

Add butter and half of the sour cream to the potatoes.

Find a large whisk and whisk everything together.

It takes some time, and you need to whisk hard. Add the sour cream a little at a time until you have the desired consistency.

Add salt and pepper and stir it well.

Taste and add more salt and pepper if needed.