1. Mix butter, cream cheese, and salt in a large bowl with hands until crumbly. Add flour, and mix until just combined. Turn out onto a lightly floured work surface, and divide in half. Shape each half into a disk; wrap each disk in plastic. Refrigerate until cold, about 4 hours or up to overnight.

2. Stir together breadcrumbs and 1/2 cup sugar in a small bowl; set aside. Stir together remaining 3 tablespoons sugar and the cinnamon in another small bowl; set aside.

3. To make filling: Put prunes and brandy in a small airtight container. Let soak at room temperature overnight. Drain prunes. Puree in a food processor until smooth. Transfer to a small bowl. Stir in breadcrumbs and sugar. Refrigerate until ready to use, up to 1 day ahead.

4. Roll 1 disk to 1/8 inch thick. Cut out a 12-inch circle. Brush beaten egg in a 1-inch border around circle. Put half the prune filling in center, and spread out to beaten egg border. Sprinkle 1/2 cup breadcrumb mixture over filling. Cut circle into 16 wedges. Starting at outside edge of each wedge, roll up into a crescent shape. Space 1 inch apart on a baking sheet lined with parchment paper. Brush with beaten egg, and sprinkle with cinnamon-sugar mixture. Repeat with remaining disk and filling. Refrigerate rugelach until cold, about 2 hours.

5. Preheat oven to 325 degrees. Bake rugelach until golden brown and cooked through, about 40 minutes. Let cool completely on wire racks. Rugelach can be stored in airtight containers at room temperature up to 3 days.