Cream butter, oil, sugars, baking soda and vanilla together until light and creamy. Stir in yogurt.
Mix the dry ingredients together in a separate bowl, and stir into the butter and yogurt mix.
It is a sticky mixture, so use a small spring loaded ice cream scoop to drop the cookie portions onto a paper lined baking tray. Top with extra dark chocolate chunks.
Place in the oven for 15-20 mins. Cooking time depends on whether you prefer a softer cookie (lighter colour in the middle) or a crispy cookie (golden brown all the way through).
