Sieve the flour and bicarbonate of soda into a large bowl. Stir in the porridge oats, cranberries, sugar and chunks of chocolate.
Gently mix the egg yolks with the melted, cooled butter and add this wet mixture to the dry ingredients. Stir until well mixed.
Use a tablespoon to scoop up some of the mixture, then use your hands to round them into small balls before flattening them slightly when you have arranged them on the baking trays. Arrange them a few centimetres apart as they will spread out a little bit while cooking.
Bake for 10 minutes or until golden brown. Transfer to a wire rack to cool before eating.