In a bowl of stand mixer, combine sifted flour and Saf instant yeast. In a separate large bowl, the rest of ingredients for the dough and whisk until sugar and salt are dissolved. Add liquid mixture to the flour. Using paddle attachment, combine all ingredients.
Knead on medium speed for about 5 minutes (for KA: speed 2 for 5 minutes + speed 4 for 2 minutes), until a very soft dough comes together.
Transfer the dough to a lightly greased bowl, cover with plastic wrap, and leave at room temperature for 1 - 1 1/2 hours, until doubled in size.
Remove the dough from the bowl and turn out onto a floured work surface. With your fingers, gently pat it to make an even layer, sprinkle with flour, and gently roll a rectangular 1/2" thick. Divide it into two halves. Let it rest for 5 minutes, covered.
Roll both halves 1/4" thick. Using a 3" D cookie cutter, mark 10-12 rounds on one of them, and spoon 1 tsp of filling in the center of each round.
Place the other half of the dough on top. Using the same cookie cutter, cut out circles around the covered filling. The edges will stick together during the process of cutting. Note: they won't stick well if you have too much flour on the inner side of the dough.
Lightly oil a baking sheet. Arrange shaped doughnuts on it leaving enough space around each one to double.
Cover and leave at room temperature for 45-60 minutes.
Fill a large shallow pot with oil 2 1/2" deep and heat it to 175C/350F. Right before frying, pierce the top and the bottom of each doughnut with a toothpick once on each side to prevent forming a bubble around the filling.
Fry for about 2 munites on each side, starting bottom (wet side) down, until dark golden brown.
Remove from oil to paper towels to drain off excess oil. Sprinkle with powdered sugar and serve.