Preheat oven to 190 degrees and line two baking trays with paper.

Cream the butter and sugars using an electric mixer until they are light and fluffy.

Add the eggs one at a time and beat well between each addition.

Stir through the vanilla and then sift the flour and bicarbonate of soda into the bowl as well and mix until just combined.

Add the dark chocolate chips and mix together.

Spoon tablespoons of mixture onto the prepared trays and leave a 2 - 3 cm gap between each biscuit to allow room for them to spread.

Place the baking trays into the oven and cook for 12 - 15 minutes or until the biscuits turn a light golden colour.

Cool the cooked biscuits on the baking trays for 5 minutes before carefully transferring to a wire rack to cool completely.