In a medium bowl, cream together the melted butter, brown sugar and caster sugar until well blended. Beat in the vanilla, egg and egg yolk until light and creamy. Mix in the sifted ingredients until just blended. Stir in the chocolate chips by hand using a wooden spoon. Drop cookie dough onto the prepared baking trays, with each cookie around 4 tablespoons of dough (for smaller cookies, drop 1 rounded tablespoonful and adjust baking time as necessary). Do not flatten the dough. Cookies should be about 8cm apart.