In a stand mixer or mixing bowl, combine all ingredients except butter and salt. Start mixing and gradually add the butter cubes. Then, add salt and knead for 12-15 minutes until the dough is smooth and elastic. Refrigerate overnight for best results, or let rise at room temperature until doubled in size.

Prepare the filling in advance and let it cool completely. Melt butter and chocolate together, then mix in the remaining ingredients until smooth.

Roll out the dough into a rectangle. Spread the chocolate filling over half the dough, fold over, and repeat. After applying the filling twice, roll out again and cut into long triangles.

Roll each triangle from the wide end to the tip, stretching the tip gently. Place rugelach on a parchment-lined baking sheet, spaced slightly apart. Bake in a preheated 320°F (160°C) convection oven for 35-40 minutes until golden.

While baking, prepare the sugar syrup. When done, brush or pour syrup over the rugelach to keep them moist. Store in an airtight container to maintain freshness.