Place butter, cream cheese, sour cream, flour, and salt in a food processor; pulse until the mixture becomes crumbly. Turn out onto a lightly floured surface and gently form into a ball. Divide the dough into 4 equal portions, flatten each into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour or overnight.

In a medium bowl, combine chopped walnuts, raisins, granulated sugar, cinnamon, and brown sugar. Mix well and set aside.

On a lightly floured surface, roll one disk of dough into a 10-inch circle about 1/8-inch thick. For easier handling, roll between two sheets of parchment paper.

If using, spread a thin layer of apricot preserves over the dough, leaving a 1/4-inch border around the edge. Sprinkle 1/4 of the filling mixture evenly over the dough, gently pressing it in.

Using a pizza cutter or sharp knife, cut the circle into 12 equal wedges (like a pizza). Starting from the wide outer edge, roll each wedge toward the pointed end. Place shaped cookies on a parchment-lined baking sheet, with the pointed end tucked underneath.

Refrigerate shaped cookies for 20 minutes. Meanwhile, preheat the oven to 350°F (175°C).

Brush each rugelach lightly with egg wash and sprinkle with cinnamon-sugar mixture. Bake for 18-22 minutes until golden brown. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

Repeat the process with the remaining dough portions and filling.