Preheat oven to 190°C/170°fan/Gas 5 and place 12 muffin cases in a muffin tin. Melt 110g (4oz) butter.
In a large mixing bowl sift plain flour, baking powder and cinnamon, then stir in caster sugar. Make a well in centre and pour in eggs, milk and melted butter. Stir until just combined, then fold in pumpkin and raisins. Spoon into muffin cases.
In a separate bowl rub remaining butter into self-raising flour then stir in demerara sugar. Sprinkle over batter in cases then bake for 30-40 minutes until risen and golden.
Leave in muffin tin for 5 minutes then cool on a wire rack. Serve warm or cold.