In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, salt, and lemon zest (if using). Add the cold butter pieces to the dry ingredients.

Using a pastry cutter or your fingertips, cut the butter into the flour mixture until it resembles coarse crumbs.

In a small bowl, beat the eggs and vanilla extract together. Add the egg mixture to the flour mixture. Mix until the dough comes together. If it's too dry, add a teaspoon of cold water at a time until it holds together.

Shape the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 1 hour.

In a medium bowl, combine the finely chopped nuts, granulated sugar, and ground cinnamon. Set aside.

Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.

Divide the chilled dough into two equal portions. On a lightly floured surface, roll out one portion into a rectangle approximately ¼ inch (6 mm) thick.

Spread a thin layer of fruit jam evenly over the dough, leaving a small border around the edges. Sprinkle half of the nut mixture evenly over the jam layer.

Starting from one of the long edges, carefully roll the dough into a tight log, similar to a jelly roll. Pinch the seams and ends to seal. Repeat with the second portion of dough and remaining filling. Place the logs seam-side down on the prepared baking sheet.

Bake in the preheated oven for 30-35 minutes, or until the rolls are golden brown.

Remove from the oven and allow the rolls to cool on the baking sheet for about 10 minutes.

While the rolls are still warm but cool enough to handle, use a sharp serrated knife to slice them diagonally into ½-inch (1.3 cm) thick cookies. Place the sliced cookies on a wire rack to cool completely.

Once cooled, dust the cookies with powdered sugar if desired.

Store any leftovers in an airtight container at room temperature for up to 1 week.