Mix the flour and butter into a paste and beat into the butternut. Add the salt, castor sugar, cinnamon, nutmeg and egg yolks and beat well.
In another bowl, beat the egg whites into soft peaks and fold into the butternut mixture.
Place 6 ramekins or cups onto a baking sheet and spray their insides with non-stick spray. Spoon the mixture into the cups and bake in the oven, preheated to 190 ºC for 20 – 25 minutes or until cooked right through.
Remove from oven and serve at once.