Pre-heat oven to 210 degrees Celsius. Prepare a baking tray with baking baking and put it to one side. Put flour in a large bowl. Add in the salt, bicarbonate of soda and cream of tartar to the flour. Cut the butter into small cubes and add it to the flour mixture and rub the butter in with your hands until all the butter is mixed in. Add the yoghurt and mix it in with a wooden spoon. When you cannot mix it anymore with the spoon use your hands to knead it in the bowl.