In a large bowl sift together flour and bicarbonate of soda, set aside.
In a separate bowl beat sugars and butter together with an electric mixer on low speed or whisk until creamed. Then add vanilla essence, eggs and egg yolk one at a time beating well in between each addition.
Fold in flour mixture slowly in 2 batches with a wooden spoon until combined.
Add chocolate (and nuts optional) all at once and knead through the dough with your fingers until fully incorporated into the mixture.
Roll out some glad wrap onto a table or board and place dough mix onto it then roll mixture into a log by twisting the ends and making a bonbon shape. Refrigerate for up to 2 hours to rest- resting is optional but I find the dough easier to cut after it's been in the fridge.
Line a baking tray with baking paper and cut 3cm portions off cookie log, roll and press flat onto the baking tray 5 cm apart to allow for spreading of mixture. Cook in a preheated oven at 180 degrees for 10-15 minutes or until done to your liking then cool on cooling rack. I pull them out when they are still doughy and slightly browned at the edges as they will harden on standing. If you have come out with a crunchy cookie, you have overcooked them.