Dissolve the sugar, salt and egg yolk in the milk, then mix in the yeast. Let it activate for about 5 to 10 minutes. Then knead with the flour and butter to form a smooth, supple dough. Cover and let rise to double size.
Roll out the dough to a thickness of 2 cm and cut out cookies approx. 6 cm in diameter. Makes about 12 pieces. Place on a fresh, floured tea towel and let rise for 20 minutes. Mix the ingredients for the filling and for sprinkling homogeneously.
Fill a large pan 1 cm high with the frying oil and heat it to 190 degrees. It's hot enough when small bubbles appear on a wooden spoon handle that you dip into the frying oil. Bake the first portion over medium heat until golden brown on both sides. Remove from the oil with a slotted spoon and allow to drain. Restore the oil level by adding deep-frying oil. Continue like this until all of the pancakes are fried.
Put some of the filling in the middle of the pancakes with the help of a piping nozzle, roll them in the sugar-cinnamon mixture and consume while warm.