Sift flour and cinnamon into a large bowl. Add caster sugar and cereal. Stir to combine. Make a well in the center.
Whisk margarine, buttermilk, eggs and vanilla together in a jug. Pour into well. Using a wooden spoon, stir until just combined. Fold through raspberries.
Spoon mixture into muffin holes. Sprinkle with demerara sugar. Bake for 15 to 20 minutes or until a toothpick inserted into the center of 1 comes out clean. Stand in pan for 5 minutes. Turn out onto a wire rack to cool. Serve.