Mix flour, sugar and yeast. Stir the dry mixture until well mix

Add the egg yolks and mashed potatoes. 

Add warm water little by little while kneading until the mixture becomes smooth.

Add melted butter and salt while kneading until the dough becomes elastic and smooth. 

Mould dough into a ball shape and put into an oil coated bowl bigger in size than the dough. Use a moist towel/napkin to cover (so that the dough does not become dry).

Rest the dough for about 20-30 mins in room temperature.

Sprinkle flour on board, remove dough and deflate it using a rolling pin.

Use a donut cutter to cut into donut shape.

After it has been formed, leave it for about 20-30 minutes to proof again in room temperature.

Fry potato donuts in oil using med heat until they turn golden brown.

Remove donuts and drain.

Allow donuts to cool down.