In large bowl, cream together the butter, brown sugar and white sugar until smooth. Beat in the eggs then stir in the creme de menthe liqueur.
Combine the flour, bicarb soda and salt; stir into the butter mixture. Mix in the chocolate chips using a wooden spoon. Drop dough by heaping teaspoonfuls onto an ungreased baking tray. Biscuits should be at least 5cm apart.
Bake for 8 to 10 minutes in the preheated oven. Allow biscuits to cool on baking tray for 5 minutes before removing to a wire rack to cool completely.