Combine yeast, and sugar in warm milk, it should be around 110°F (43°C). You should be able to put your finger in the milk, if not then it’s too hot. Cover with towel, and set aside and allow the yeast to activate and rise, about 5-10minutes in a warm area of your kitchen.
Meanwhile, in a large bowl, sift flour, sugar, and salt. Add butter, and break it into small pea-size into the flour using a pastry blender or your fingers. Add yolks and yeast mixture into the flour and combine with a wooden spoon.
Gradually add 1/2 cup of warm milk, and work the dough together with your hands until the dough leaves the sides of the bowl clean. It may vary as to the amount of milk to add, more than 1/2 cup or less. You don't want the dough to be too sticky.
Place the dough on a lightly dusted counter and knead for about 5-10 minutes, to the point when it becomes smooth, soft and you can hear the bubbles popping as you knead.
Place dough in a clean bowl, sprinkled with flour and cover with plastic wrap and a towel to avoid any drafts. Let rise in a warm place for about 1 hour, or until it doubles in size.
Lay dough onto a floured board. Now, you have options of making twisted doughnuts, regular whole doughnuts or heart-shape doughnuts.
For twisted doughnuts, I separate the dough by cutting the dough into 12 equal pieces. Roll out each piece into tube shape, about 12 inches in length. Take the tube dough with your hands and fold the dough in half and bring the ends together, then begin twisting the dough together.For whole or heart-shape doughnuts, roll out the dough to about 2 cm or 1/2 inch thickness, and cut your shapes using a cookie cutter. Lay the cut or twisted shaped doughnuts onto a baking sheet, lined with parchment paper, cover with towel and allow the doughnuts to rise for about 40-45 minutes.
When doughnuts are ready, heat oil to 350°F in a large saucepan, cast iron pan or a deep fryer. It's important to note, whatever you use, make sure there is enough oil below the doughnut, so when you place the doughnuts into the oil, they don't touch the bottom of the pan, as this will avoid them from burning.
Carefully place 3-4 doughnuts at a time into the hot oil, and for about 30-40 seconds on each side until golden in colour. Remove and place on paper towel to absorb any excess oil.
Once the doughnuts have just about cooled, place the cinnamon or sugar mixture into a brown bag, place the doughnut inside the bag and gently toss. Make sure the top of bag is tightly closed before tossing. If they are too warm the sugar will melt and if too cold the sugar won't stick to the doughnuts. If you are making the whole or heart-shape doughnuts, sprinkle with icing sugar.
Enjoy!!