Rub cold butter and cream cheese into bits. In food processor pulse flour, salt, butter, cream cheese and soured cream until crumbly.
Shape crumbly mixture into four equal disks. Wrap each disk and chill 2 hours or up to 2 days.
Roll each disk into a 23cm round, keeping other disks chilled until ready to roll them.
Combine sugar, cinnamon, walnuts and sultanas.
Sprinkle each round with sugar/nut mixture. Press lightly into dough. With chef's knife or pizza cutter, cut each round into 12 wedges. Roll wedges from wide to narrow (you will end up with point on outside of biscuit). Place on ungreased baking trays and chill rugelach 20 minutes before baking.
Preheat oven to 180 C.
After rugelach are chilled, bake them in the centre rack of the oven for 20 to 25 minutes until lightly golden. Cool on wire racks. Store in airtight containers. They freeze very well.
Variations: Before putting the filling on the dough, use a pastry brush to layer apricot jam and dark brown soft sugar. Then add the recommended filling. You may also make a mixture of cinnamon and sugar and roll the outside of the rugelach in this prior to putting them on the baking trays.