Pulse the flour and salt together in a food processor to combine. Add the cold cubed butter and pulse until the mixture looks like coarse crumbs.

Add the sour cream, egg yolk, and brandy if using. Pulse until the dough just comes together in shaggy clumps, it shouldn't form a smooth ball yet.

Turn the dough onto a lightly floured surface and divide it into two disks. Wrap each in plastic and chill for 45 minutes.

Stir the ground walnuts, sugar, and cinnamon together in a bowl. Set aside until ready to fill the dough.

Heat the oven to 180 C / 350 F and line two 33 x 46 cm / 13 x 18 inch sheet pans with parchment.

Roll one dough disk on a floured surface into a 28 cm / 11-inch circle, about 3 mm thick. Cut into 12 wedges with a sharp knife or pizza cutter.

Spread a thin layer of apricot jam over each wedge, then sprinkle with the walnut filling, leaving the pointed tip bare.

Roll each wedge from the wide edge toward the point, then curve the ends inward to form a crescent. Place on the sheet pan, point tucked underneath.

Repeat rolling, filling, and shaping with the second dough disk. You'll get about 20 to 24 crescents total.

Bake one pan at a time for 16 to 18 minutes, until the crescents are golden brown on top and the undersides are pale gold, not dark.

Cool on the pan for 5 minutes, then while still warm, roll each crescent in powdered sugar until fully coated.

Transfer to a wire rack to cool completely before serving or storing.