1. Preheat oven to 200°C (400°F). Line a baking sheet with parchment paper.

2. In a large bowl, cream together softened butter, granulated sugar, vanilla sugar, and salt until light and fluffy. Add flour and potato starch in two batches, mixing just until a soft dough forms. Knead briefly on a floured surface, then wrap and chill for 30 minutes.

3. Divide almond paste into two equal portions. Roll each into a cylinder about 40 cm (16 inches) long.

4. Remove dough from refrigerator. Divide into two equal parts. Roll each into a rectangle approximately 10 x 40 cm (4 x 16 inches). Place one almond paste cylinder along the long edge of each dough strip. Roll up tightly to enclose, pinching seams to seal. Place seam-side down on prepared baking sheet, spaced at least 5 cm (2 inches) apart.

5. Bake for 15 minutes, or until golden at the edges and firm to the touch. Remove from oven and let cool on the sheet for 5 minutes.

6. While cakes bake, prepare meringue: whisk egg whites until stiff peaks form. Gradually add any remaining granulated sugar, beating until glossy and firm.

7. Spoon or pipe meringue generously over the top of each cake, covering the surface completely.

8. Return to oven and bake for 8–10 minutes, or until meringue is puffed and golden brown.

9. Let rest for 10 minutes before slicing. Serve slightly warm or at room temperature.