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.

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.

Slice the rolls diagonally into ½-inch (1.3 cm) thick cookies. Place the sliced cookies on a wire rack to cool completely.

Dust with powdered sugar if desired before serving.