Preheat the oven to 190°C/375°F/Gas mark 5. Line two baking trays with baking parchment.
Cream the butter and sugars in a bowl with an electric beater until light and fluffy.
Gradually add the eggs, beating well after each addition. Stir in the vanilla, then the sifted flour and bicarbonate of soda until just combined. Mix in the chocolate chips and pecan nuts.
Drop tablespoonfuls of the mixture onto the trays, leaving room for spreading. Bake the cookies for 8–10 minutes until lightly golden. Cool slightly on the trays before transferring to a wire rack to cool completely.