In a saucepan, bring the stock to a boil with the pumpkin.
Meanwhile, in a pressure cooker, saute the shallots and sage leaves in butter. Pour in half the glass of wine. When the wine has evaporated, add the rice, stirring to coat. Add remaining wine and let evaporate. Pour in the stock (reserving pumpkin), season to taste and stir well.
Place the slices of pumpkin on top of the rice without stirring. Close the pressure cooker and set on maximum pressure. Cook 4 minutes from the time the cooker reaches pressure.
Release pressure and carefully remove lid. Remove the slices of pumpkin and mash with a fork. Add back to the rice, stir well and sprinkle with nutmeg. Add the butter and stir. Serve, garnished with Parmesan and pepper.