Preheat the oven to 180 degrees. Grease the donut moulds.
Beat the eggs and sugar until the mixture becomes fluffy. Add the vanilla flavor. Melt the butter over heat and add it to the egg mixture. Combine with a mixer. Mix the Čakovec mlinovi flour, baking powder and salt. Add half the amount to the egg mixture and combine with a mixer at the lowest speed. Add yogurt and milk. Mix everything until well combined. Add the remaining flour and combine.
Pour the donut mixture into a decorating bag or freezer bag with a tip cut off. Use the bag to fill the moulds by filling 3/4 of each mould. Bake the donuts for 15 minutes or until the toothpick stuck in one of your donuts comes out dry.
Leave the baked donuts in moulds for a few minutes and transfer them to the grill to cool. If you're going to sprinkle them with sugar, do it while they're warm. Make the icing when the donuts are cool.