Place flour, salt, and baking powder in a medium bowl and whisk to combine. Add cottage cheese and ground almonds. Use a pastry cutter or rub the mixture between your fingers to blend cottage cheese and flour until it resembles coarse meal. Add sour cream and combine well using a large spoon

Cut a well chilled stick of butter into small cubes, about 1/4" in size. Spoon the mixture, together with the butter, into a large zip-lock bag. Expel any air from the bag and close it. Place the bag in the freezer for about 10 minutes

Remove the dough from the freezer. Use a rolling pin to flatten the butter into flakes. Place the bag back in the freezer for about 10-20 minutes

Holding both ends of the bag opening with your fingers, knead the mixture by alternately pressing it, from the outside of the bag, with knuckles and heels of your hands until the mixture holds together in one piece

Wrap the dough with plastic wrap, flatten it into a disc and refrigerate for 20-45 minutes

Preheat oven to 425F

Take the dough out from the bag and place onto a lightly floured surface. Using a large rolling pin, roll out the dough to about 10 x 18 inch rectangle, making sure the dough is at least 1/4" thick

Spread the filling and sliced apples evenly across the entire surface of the rolled out dough

Starting with the the shorter side, roll up into a roll

Slice into about 1" pieces and place on the parchment paper lined backing sheet

Whisk one egg with a tsp of milk or cream until pale yellow and perfectly mixed. Using a pastry brush paint the rolls with a light, even coat of egg wash

Bake at 425F for 15 minutes, turn the temperature to 410F and bake for another 10-15 minutes, until golden brown