Method

1. Make the Plain Shortbread. In a medium sized bowl using a hand-held mixer, beat the vegan butter and Natvia together. Sift in the flour and salt and on low speed, beat to form a dough.  Use your hands to bring the mixture together into a large ball.  Wrap with plastic wrap and press it down to form a thick disc.  Place in the fridge for 15 minutes to chill and firm.
2. Make the Chocolate Shortbread. In the same medium sized bowl, beat the vegan butter and Natvia together. Sift in the flour, cacao powder and salt and on low speed, beat to form a dough.  Use your hands to bring the mixture together into a large ball.  Wrap with plastic wrap and press it down to form a thick disc.  Place in the fridge for 15 minutes to chill and firm.
3. Preheat the oven to 150°C/ 302°F and line two baking trays with grease proof paper.
4. To assemble, take the plain shortbread out of the fridge, leaving the chocolate one in there, unwrap it and place on a rectangle sheet of grease proof paper. Place the plastic wrap on top of the shortbread and roll to a 19 cm x 25 cm (7.4 in x 9.8 in) rectangle that’s ½ cm thick.  I found using the plastic wrap as a protective shield prevented the rolling pin from sticking to the dough.
5. Take the chocolate shortbread from the fridge and follow the same procedure as above. Carefully place the chocolate rectangle on top of the plain rectangle.  Gently using the rolling pin, roll together so they stick.
6. Carefully roll the rectangles together like a Swiss roll to form a 25cm long log. Use the baking paper to help and support to create a tight roll.  Slice the log into 1cm thick cookies and place on the baking trays.  Bake for 25-30 minutes.  They should be slightly golden on the outside.  Leave to cool on the trays for 10 minutes before removing to a wire rack to cool completely.