1. Preheat your oven to 320⁰F (160⁰C).
2. Line a large baking tray with parchment paper.
3. Lightly grease a plate with non-stick spray.
4. Spoon teaspoonfuls of the 1 x 350 g bottle of Nutella spread onto the plate. Place in the freezer for 1 hour until firm.
5. Keep the Nutella portions frozen until needed. Work with only a few at a time because they soften quickly. If they start melting, return them to the freezer before continuing.
6. In a large mixing bowl, cream together the 250 g butter and 1/2 cup brown sugar for about 3 minutes until light and creamy.
7. Add the 1/4 cup golden syrup and 1 tsp vanilla essence and beat until combined.
8. Add the 2 large eggs, one at a time, beating well after each addition.
9. Sift together the 2 cups of cake flour, 1 tsp bicarbonate of soda, and 1 cup cocoa powder.
10. Add the dry ingredients to the butter mixture and mix until a soft dough forms. If the dough feels very soft, chill it for 15 to 20 minutes before rolling.
11. Roll the dough into walnut-sized balls.
12. Flatten each ball slightly in your palm.
13. Place one frozen Nutella portion in the centre and carefully wrap the dough around it. Roll gently until sealed completely.
14. Arrange the dough balls on the prepared baking tray, leaving space between them. Flatten each one slightly with your finger.
15. Lightly grind a little coarse sea salt over the tops.
16. Bake for 10 to 12 minutes.
17. The biscuits should look set around the edges but still slightly soft in the centre.
18. Leave on the tray for 5 minutes before transferring to a wire rack to cool completely.
19. Store in an airtight container once fully cooled.

Baking time of approximately 36 minutes represents 3 baking trays, thus roughly 12 minutes per tray