Preheat the oven to 180°C. Line 2 large baking sheets with baking paper and grease with nonstick spray.
1. Put the butter, vanilla essence, eggs and sugar in a mixing bowl and beat with an electric beater until combined. Add the flour, bicarbonate of soda, salt and chocolate and mix until a soft dough forms.
2. Roll the dough into a ball and chill in the fridge for at least 30 minutes.