In a large mixing bowl, whisk together the flour, 1/2 cup sugar, baking powder, and salt. Use a pastry cutter or fork to work the cold butter into the dry ingredients until the mixture resembles coarse crumbs.

In a separate small bowl, whisk the eggs, sour cream, and vanilla extract. Add the wet ingredients to the flour mixture and stir until a soft dough forms. Divide the dough into two equal disks, wrap in plastic, and refrigerate for at least 1 hour.

Preheat the oven to 350°F (175°C) and line two large baking sheets with parchment paper.

Prepare the filling: In a medium bowl, combine the ground walnuts, 3/4 cup sugar, cinnamon, orange zest, honey, and milk. Stir until the mixture is well-incorporated and holds together slightly.

On a lightly floured surface, roll one disk of dough into a rectangle approximately 1/8-inch thick (roughly 10x12 inches).

Spread half of the nut filling evenly over the dough, leaving a 1/2-inch border at the edges. Press the filling down gently with your hands.

Starting from the long side, roll the dough tightly into a log. Repeat with the second disk and remaining filling.

Using a sharp knife, slice the logs into 1-inch wide pieces. Place the cookies on the prepared baking sheets, spaced 1 inch apart.

Bake for 18–22 minutes, or until the edges are lightly golden and the pastry is set.

Transfer to a wire rack to cool completely. Once cooled, dust generously with powdered sugar before serving.