Preheat oven to 180°C. Brush six large (250ml/1-cup) non-stick muffin pans with the melted butter to lightly grease.
Use electric beaters to beat the sugar, chestnut puree, eggs and orange rind in a medium bowl until smooth. Add 125ml (1/2 cup) of the orange juice and the oil, and beat to combine. Stir in the pumpkin.
Sift flour over pumpkin mixture and use a large metal spoon to fold in until just combined.
Spoon the mixture evenly into the greased pans. Bake in preheated oven for 35-40 minutes or until a skewer inserted in the centres of the muffins comes out clean. Set aside for 5 minutes and then turn onto a wire rack. Serve warm or at room temperature.
