1) Pulse the flour, sugar and salt in food processor until combined. Add the butter and pulse about 20 times, until it resembles coarse sand with some pea-sized pieces of butter.
2) Add the cream cheese and sour cream, and pulse until it comes together in a rough dough (with some uneven pebbles sized-pieces).
3) Turn the dough out onto a floured work surface and divide into 4 equal portions. Pat each portion into a flat square and wrap in cling film. Freeze dough for 15 minutes.
For the filling:
1) Chop the nuts in a clean food processor. Add the apricot jam, sultanas and salt; puree to make a very smooth paste.
1) Roll a portion of dough into a 15 ¼-cm by 35 ½-cm rectangle about ¾-cm thick. (Don't worry about slightly rough edges; these will be rolled inside of the rugalach.)
2) Spread 1/4 of the filling over the surface with a small spatula. Starting with a long side, roll the dough up into a tight cylinder ending with the seam on the bottom. Press the top slightly to flatten. Wrap in cling film and freeze for another 15 minutes. Repeat with the remaining dough and filling. (The cylinders can be frozen for up to a month.)
1) Evenly position the racks in the oven and preheat to 190C/Gas Mark 5.
2) Line 2 baking sheets with parchment or silicone baking mats.
3) Slice the cylinders into 4-cm pieces, and place rugalach seam-side down on the prepared pans.
3) Whisk the egg yolks together and brush this glaze over the top of each rugalach. Sprinkle with sugar and bake for about 25 minutes until pale golden and crispy on top.
4) Remove from oven and let cool slightly on the baking sheet. Then carefully transfer to a wire rack to cool. Serve.
Store rugalach in a tightly sealed container for up to 3 days.