Boil your potato and mash it.

Mix together flour, sugar, yeast, egg yolks, and mashed potato, you can use hand mixer (use the hook paddle for bread) to do this or simply just use your clean bare hand to knead it. Add the mixture of milk and condensed milk little by little into the dough until all poured in.

Knead the dough until half kneaded and then add the salted butter and salt. Continue to knead the dough until it fully kneaded. How to make sure that the dough is fully kneaded? You could see the dough become all united and looked smoother at the surface.

Measure the dough about 50 gr each. Round the dough one by one, and put in on a baking paper that already dusted by a flour. Let the dough rest about 20 minutes and covered by napkins on top.

After 20 minutes, check the dough, the size become 2x bigger than before. Press each dough with small preasure, just to make it flatten a bit, and cut the middle with bottle cap or something round to make it look like a ring. Continue rest the dough for another 15 minutes.

You could whisk the salted butter with a teaspoon of condensed milk until not firm anymore or has a smooth texture and dip your doughnut half in it, and continue to dip it again in chocolate sprinkles. Or you could simply just dust it with some icing sugar or even cinnamon icing sugar. Kids are gonna love it!